refactor: merge bedrock-apikey into bedrock with auth_mode credential

Consolidate two separate channel types (bedrock + bedrock-apikey) into
a single "AWS Bedrock" channel. Authentication mode is now distinguished
by credentials.auth_mode ("sigv4" | "apikey") instead of separate types.

Backend:
- Remove AccountTypeBedrockAPIKey constant
- IsBedrock() simplified; IsBedrockAPIKey() checks auth_mode
- Add IsAPIKeyOrBedrock() helper to eliminate repeated type checks
- Extend pool mode, quota scheduling, and billing to bedrock
- Add RetryableOnSameAccount to handleBedrockUpstreamErrors
- Add "bedrock" scope to Beta Policy for independent control

Frontend:
- Merge two buttons into one "AWS Bedrock" with auth mode radio
- Badge displays "Anthropic | AWS"
- Pool mode and quota limit UI available for bedrock
- Quota display in account list (usage bars, capacity badges, reset)
- Remove all bedrock-apikey type references

frontend/src/components/account/AccountCapacityCell.vue

@@ -292,17 +292,19 @@ const rpmTooltip = computed(() => {
   }
 })
 
-// 是否显示各维度配额（仅 apikey 类型）
+// 是否显示各维度配额（apikey / bedrock 类型）
+const isQuotaEligible = computed(() => props.account.type === 'apikey' || props.account.type === 'bedrock')
+
 const showDailyQuota = computed(() => {
-  return props.account.type === 'apikey' && (props.account.quota_daily_limit ?? 0) > 0
+  return isQuotaEligible.value && (props.account.quota_daily_limit ?? 0) > 0
 })
 
 const showWeeklyQuota = computed(() => {
-  return props.account.type === 'apikey' && (props.account.quota_weekly_limit ?? 0) > 0
+  return isQuotaEligible.value && (props.account.quota_weekly_limit ?? 0) > 0
 })
 
 const showTotalQuota = computed(() => {
-  return props.account.type === 'apikey' && (props.account.quota_limit ?? 0) > 0
+  return isQuotaEligible.value && (props.account.quota_limit ?? 0) > 0
 })
 
 // 格式化费用显示