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

backend/internal/service/account.go

@@ -656,7 +656,7 @@ func (a *Account) IsCustomErrorCodesEnabled() bool {
 // IsPoolMode 检查 API Key 账号是否启用池模式。
 // 池模式下，上游错误不标记本地账号状态，而是在同一账号上重试。
 func (a *Account) IsPoolMode() bool {
-	if a.Type != AccountTypeAPIKey || a.Credentials == nil {
+	if !a.IsAPIKeyOrBedrock() || a.Credentials == nil {
 		return false
 	}
 	if v, ok := a.Credentials["pool_mode"]; ok {
@@ -771,11 +771,16 @@ func (a *Account) IsInterceptWarmupEnabled() bool {
 }
 
 func (a *Account) IsBedrock() bool {
-	return a.Platform == PlatformAnthropic && (a.Type == AccountTypeBedrock || a.Type == AccountTypeBedrockAPIKey)
+	return a.Platform == PlatformAnthropic && a.Type == AccountTypeBedrock
 }
 
 func (a *Account) IsBedrockAPIKey() bool {
-	return a.Platform == PlatformAnthropic && a.Type == AccountTypeBedrockAPIKey
+	return a.IsBedrock() && a.GetCredential("auth_mode") == "apikey"
+}
+
+// IsAPIKeyOrBedrock 返回账号类型是否支持配额和池模式等特性
+func (a *Account) IsAPIKeyOrBedrock() bool {
+	return a.Type == AccountTypeAPIKey || a.Type == AccountTypeBedrock
 }
 
 func (a *Account) IsOpenAI() bool {