feat(antigravity): add 403 forbidden status detection, classification and display

Backend:
- Detect and classify 403 responses into three types:
  validation (account needs Google verification),
  violation (terms of service / banned),
  forbidden (generic 403)
- Extract verification/appeal URLs from 403 response body
  (structured JSON parsing with regex fallback)
- Add needs_verify, is_banned, needs_reauth, error_code fields
  to UsageInfo (omitempty for zero impact on other platforms)
- Handle 403 in request path: classify and permanently set account error
- Save validation_url in error_message for degraded path recovery
- Enrich usage with account error on both success and degraded paths
- Add singleflight dedup for usage requests with independent context
- Differentiate cache TTL: success/403 → 3min, errors → 1min
- Return degraded UsageInfo instead of HTTP 500 on quota fetch errors

Frontend:
- Display forbidden status badges with color coding (red for banned,
  amber for needs verification, gray for generic)
- Show clickable verification/appeal URL links
- Display needs_reauth and degraded error states in usage cell
- Add Antigravity tier label badge next to platform type

Tests:
- Comprehensive unit tests for classifyForbiddenType (7 cases)
- Unit tests for extractValidationURL (8 cases including unicode escapes)
- Integration test for FetchQuota forbidden path

frontend/src/components/account/AccountUsageCell.vue

@@ -36,6 +36,10 @@
 
       <!-- Usage data -->
       <div v-else-if="usageInfo" class="space-y-1">
+        <!-- API error (degraded response) -->
+        <div v-if="usageInfo.error" class="text-xs text-amber-600 dark:text-amber-400 truncate max-w-[200px]" :title="usageInfo.error">
+          {{ usageInfo.error }}
+        </div>
         <!-- 5h Window -->
         <UsageProgressBar
           v-if="usageInfo.five_hour"
@@ -189,8 +193,53 @@
         </span>
       </div>
 
+      <!-- Forbidden state (403) -->
+      <div v-if="isForbidden" class="space-y-1">
+        <span
+          :class="[
+            'inline-block rounded px-1.5 py-0.5 text-[10px] font-medium',
+            forbiddenBadgeClass
+          ]"
+        >
+          {{ forbiddenLabel }}
+        </span>
+        <div v-if="validationURL" class="flex items-center gap-1">
+          <a
+            :href="validationURL"
+            target="_blank"
+            rel="noopener noreferrer"
+            class="text-[10px] text-blue-600 hover:text-blue-800 hover:underline dark:text-blue-400 dark:hover:text-blue-300"
+            :title="t('admin.accounts.openVerification')"
+          >
+            {{ t('admin.accounts.openVerification') }}
+          </a>
+          <button
+            type="button"
+            class="text-[10px] text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200"
+            :title="t('admin.accounts.copyLink')"
+            @click="copyValidationURL"
+          >
+            {{ linkCopied ? t('admin.accounts.linkCopied') : t('admin.accounts.copyLink') }}
+          </button>
+        </div>
+      </div>
+
+      <!-- Needs reauth (401) -->
+      <div v-else-if="needsReauth" class="space-y-1">
+        <span class="inline-block rounded px-1.5 py-0.5 text-[10px] font-medium bg-orange-100 text-orange-700 dark:bg-orange-900/40 dark:text-orange-300">
+          {{ t('admin.accounts.needsReauth') }}
+        </span>
+      </div>
+
+      <!-- Degraded error (non-403, non-401) -->
+      <div v-else-if="usageInfo?.error" class="space-y-1">
+        <span class="inline-block rounded px-1.5 py-0.5 text-[10px] font-medium bg-amber-100 text-amber-700 dark:bg-amber-900/40 dark:text-amber-300">
+          {{ usageErrorLabel }}
+        </span>
+      </div>
+
       <!-- Loading state -->
-      <div v-if="loading" class="space-y-1.5">
+      <div v-else-if="loading" class="space-y-1.5">
         <div class="flex items-center gap-1">
           <div class="h-3 w-[32px] animate-pulse rounded bg-gray-200 dark:bg-gray-700"></div>
           <div class="h-1.5 w-8 animate-pulse rounded-full bg-gray-200 dark:bg-gray-700"></div>
@@ -816,6 +865,51 @@ const hasIneligibleTiers = computed(() => {
   return Array.isArray(ineligibleTiers) && ineligibleTiers.length > 0
 })
 
+// Antigravity 403 forbidden 状态
+const isForbidden = computed(() => !!usageInfo.value?.is_forbidden)
+const forbiddenType = computed(() => usageInfo.value?.forbidden_type || 'forbidden')
+const validationURL = computed(() => usageInfo.value?.validation_url || '')
+
+// 需要重新授权（401）
+const needsReauth = computed(() => !!usageInfo.value?.needs_reauth)
+
+// 降级错误标签（rate_limited / network_error）
+const usageErrorLabel = computed(() => {
+  const code = usageInfo.value?.error_code
+  if (code === 'rate_limited') return t('admin.accounts.rateLimited')
+  return t('admin.accounts.usageError')
+})
+
+const forbiddenLabel = computed(() => {
+  switch (forbiddenType.value) {
+    case 'validation':
+      return t('admin.accounts.forbiddenValidation')
+    case 'violation':
+      return t('admin.accounts.forbiddenViolation')
+    default:
+      return t('admin.accounts.forbidden')
+  }
+})
+
+const forbiddenBadgeClass = computed(() => {
+  if (forbiddenType.value === 'validation') {
+    return 'bg-yellow-100 text-yellow-700 dark:bg-yellow-900/40 dark:text-yellow-300'
+  }
+  return 'bg-red-100 text-red-700 dark:bg-red-900/40 dark:text-red-300'
+})
+
+const linkCopied = ref(false)
+const copyValidationURL = async () => {
+  if (!validationURL.value) return
+  try {
+    await navigator.clipboard.writeText(validationURL.value)
+    linkCopied.value = true
+    setTimeout(() => { linkCopied.value = false }, 2000)
+  } catch {
+    // fallback: ignore
+  }
+}
+
 const loadUsage = async () => {
   if (!shouldFetchUsage.value) return
 

frontend/src/components/layout/TablePageLayout.vue

@@ -84,9 +84,7 @@ onUnmounted(() => {
 }
 
 .table-scroll-container :deep(th) {
-  /* 表头高度和文字加粗优化 */
-  @apply px-5 py-4 text-left text-sm font-bold text-gray-900 dark:text-white border-b border-gray-200 dark:border-dark-700;
-  @apply uppercase tracking-wider; /* 让表头更有设计感 */
+  @apply px-5 py-4 text-left text-sm font-medium text-gray-600 dark:text-dark-300 border-b border-gray-200 dark:border-dark-700;
 }
 
 .table-scroll-container :deep(td) {

frontend/src/i18n/locales/en.ts

@@ -2524,7 +2524,16 @@ export default {
         unlimited: 'Unlimited'
       },
       ineligibleWarning:
-        'This account is not eligible for Antigravity, but API forwarding still works. Use at your own risk.'
+        'This account is not eligible for Antigravity, but API forwarding still works. Use at your own risk.',
+      forbidden: 'Forbidden',
+      forbiddenValidation: 'Verification Required',
+      forbiddenViolation: 'Violation Ban',
+      openVerification: 'Open Verification Link',
+      copyLink: 'Copy Link',
+      linkCopied: 'Link Copied',
+      needsReauth: 'Re-auth Required',
+      rateLimited: 'Rate Limited',
+      usageError: 'Fetch Error'
     },
 
     // Scheduled Tests

frontend/src/i18n/locales/zh.ts

@@ -1980,6 +1980,15 @@ export default {
       },
       ineligibleWarning:
         '该账号无 Antigravity 使用权限，但仍能进行 API 转发。继续使用请自行承担风险。',
+      forbidden: '已封禁',
+      forbiddenValidation: '需要验证',
+      forbiddenViolation: '违规封禁',
+      openVerification: '打开验证链接',
+      copyLink: '复制链接',
+      linkCopied: '链接已复制',
+      needsReauth: '需要重新授权',
+      rateLimited: '限流中',
+      usageError: '获取失败',
       form: {
         nameLabel: '账号名称',
         namePlaceholder: '请输入账号名称',

frontend/src/types/index.ts

@@ -769,6 +769,21 @@ export interface AccountUsageInfo {
   gemini_pro_minute?: UsageProgress | null
   gemini_flash_minute?: UsageProgress | null
   antigravity_quota?: Record<string, AntigravityModelQuota> | null
+  // Antigravity 403 forbidden 状态
+  is_forbidden?: boolean
+  forbidden_reason?: string
+  forbidden_type?: string   // "validation" | "violation" | "forbidden"
+  validation_url?: string   // 验证/申诉链接
+
+  // 状态标记（后端自动推导）
+  needs_verify?: boolean    // 需要人工验证（forbidden_type=validation）
+  is_banned?: boolean       // 账号被封（forbidden_type=violation）
+  needs_reauth?: boolean    // token 失效需重新授权（401）
+
+  // 机器可读错误码：forbidden / unauthenticated / rate_limited / network_error
+  error_code?: string
+
+  error?: string            // usage 获取失败时的错误信息
 }
 
 // OpenAI Codex usage snapshot (from response headers)

frontend/src/views/admin/AccountsView.vue

@@ -171,7 +171,15 @@
             <span v-else class="text-sm text-gray-400 dark:text-dark-500">-</span>
           </template>
           <template #cell-platform_type="{ row }">
-            <PlatformTypeBadge :platform="row.platform" :type="row.type" :plan-type="row.credentials?.plan_type" :privacy-mode="row.extra?.privacy_mode" />
+            <div class="flex flex-wrap items-center gap-1">
+              <PlatformTypeBadge :platform="row.platform" :type="row.type" :plan-type="row.credentials?.plan_type" :privacy-mode="row.extra?.privacy_mode" />
+              <span
+                v-if="getAntigravityTierLabel(row)"
+                :class="['inline-block rounded px-1.5 py-0.5 text-[10px] font-medium', getAntigravityTierClass(row)]"
+              >
+                {{ getAntigravityTierLabel(row) }}
+              </span>
+            </div>
           </template>
           <template #cell-capacity="{ row }">
             <AccountCapacityCell :account="row" />
@@ -794,6 +802,40 @@ const { pause: pauseAutoRefresh, resume: resumeAutoRefresh } = useIntervalFn(
   { immediate: false }
 )
 
+// Antigravity 订阅等级辅助函数
+function getAntigravityTierFromRow(row: any): string | null {
+  if (row.platform !== 'antigravity') return null
+  const extra = row.extra as Record<string, unknown> | undefined
+  if (!extra) return null
+  const lca = extra.load_code_assist as Record<string, unknown> | undefined
+  if (!lca) return null
+  const paid = lca.paidTier as Record<string, unknown> | undefined
+  if (paid && typeof paid.id === 'string') return paid.id
+  const current = lca.currentTier as Record<string, unknown> | undefined
+  if (current && typeof current.id === 'string') return current.id
+  return null
+}
+
+function getAntigravityTierLabel(row: any): string | null {
+  const tier = getAntigravityTierFromRow(row)
+  switch (tier) {
+    case 'free-tier': return t('admin.accounts.tier.free')
+    case 'g1-pro-tier': return t('admin.accounts.tier.pro')
+    case 'g1-ultra-tier': return t('admin.accounts.tier.ultra')
+    default: return null
+  }
+}
+
+function getAntigravityTierClass(row: any): string {
+  const tier = getAntigravityTierFromRow(row)
+  switch (tier) {
+    case 'free-tier': return 'bg-gray-100 text-gray-600 dark:bg-gray-700 dark:text-gray-300'
+    case 'g1-pro-tier': return 'bg-blue-100 text-blue-600 dark:bg-blue-900/40 dark:text-blue-300'
+    case 'g1-ultra-tier': return 'bg-purple-100 text-purple-600 dark:bg-purple-900/40 dark:text-purple-300'
+    default: return ''
+  }
+}
+
 // All available columns
 const allColumns = computed(() => {
   const c = [