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/views/admin/SettingsView.vue

@@ -1745,7 +1745,7 @@ const betaPolicyForm = reactive({
   rules: [] as Array<{
     beta_token: string
     action: 'pass' | 'filter' | 'block'
-    scope: 'all' | 'oauth' | 'apikey'
+    scope: 'all' | 'oauth' | 'apikey' | 'bedrock'
     error_message?: string
   }>
 })
@@ -2297,7 +2297,8 @@ const betaPolicyActionOptions = computed(() => [
 const betaPolicyScopeOptions = computed(() => [
   { value: 'all', label: t('admin.settings.betaPolicy.scopeAll') },
   { value: 'oauth', label: t('admin.settings.betaPolicy.scopeOAuth') },
-  { value: 'apikey', label: t('admin.settings.betaPolicy.scopeAPIKey') }
+  { value: 'apikey', label: t('admin.settings.betaPolicy.scopeAPIKey') },
+  { value: 'bedrock', label: t('admin.settings.betaPolicy.scopeBedrock') }
 ])
 
 // Beta Policy 方法