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/admin/account/AccountActionMenu.vue

@@ -76,7 +76,7 @@ const hasRecoverableState = computed(() => {
   return props.account?.status === 'error' || Boolean(isRateLimited.value) || Boolean(isOverloaded.value) || Boolean(isTempUnschedulable.value)
 })
 const hasQuotaLimit = computed(() => {
-  return props.account?.type === 'apikey' && (
+  return (props.account?.type === 'apikey' || props.account?.type === 'bedrock') && (
     (props.account?.quota_limit ?? 0) > 0 ||
     (props.account?.quota_daily_limit ?? 0) > 0 ||
     (props.account?.quota_weekly_limit ?? 0) > 0