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/settings_view.go

@@ -198,16 +198,17 @@ const (
 	BetaPolicyActionFilter = "filter" // 过滤，从 beta header 中移除该 token
 	BetaPolicyActionBlock  = "block"  // 拦截，直接返回错误
 
-	BetaPolicyScopeAll    = "all"    // 所有账号类型
-	BetaPolicyScopeOAuth  = "oauth"  // 仅 OAuth 账号
-	BetaPolicyScopeAPIKey = "apikey" // 仅 API Key 账号
+	BetaPolicyScopeAll     = "all"     // 所有账号类型
+	BetaPolicyScopeOAuth   = "oauth"   // 仅 OAuth 账号
+	BetaPolicyScopeAPIKey  = "apikey"  // 仅 API Key 账号
+	BetaPolicyScopeBedrock = "bedrock" // 仅 AWS Bedrock 账号
 )
 
 // BetaPolicyRule 单条 Beta 策略规则
 type BetaPolicyRule struct {
 	BetaToken    string `json:"beta_token"`              // beta token 值
 	Action       string `json:"action"`                  // "pass" | "filter" | "block"
-	Scope        string `json:"scope"`                   // "all" | "oauth" | "apikey"
+	Scope        string `json:"scope"`                   // "all" | "oauth" | "apikey" | "bedrock"
 	ErrorMessage string `json:"error_message,omitempty"` // 自定义错误消息 (action=block 时生效)
 }