feat(antigravity): comprehensive enhancements - model mapping, rate limiting, scheduling & ops

Key changes:
- Upgrade model mapping: Opus 4.5 → Opus 4.6-thinking with precise matching
- Unified rate limiting: scope-level → model-level with Redis snapshot sync
- Load-balanced scheduling by call count with smart retry mechanism
- Force cache billing support
- Model identity injection in prompts with leak prevention
- Thinking mode auto-handling (max_tokens/budget_tokens fix)
- Frontend: whitelist mode toggle, model mapping validation, status indicators
- Gemini session fallback with Redis Trie O(L) matching
- Ops: enhanced concurrency monitoring, account availability, retry logic
- Migration scripts: 049-051 for model mapping unification

backend/internal/service/ops_retry.go

@@ -576,7 +576,7 @@ func (s *OpsService) executeWithAccount(ctx context.Context, reqType opsRetryReq
 			action = "streamGenerateContent"
 		}
 		if account.Platform == PlatformAntigravity {
-			_, err = s.antigravityGatewayService.ForwardGemini(ctx, c, account, modelName, action, errorLog.Stream, body)
+			_, err = s.antigravityGatewayService.ForwardGemini(ctx, c, account, modelName, action, errorLog.Stream, body, false)
 		} else {
 			_, err = s.geminiCompatService.ForwardNative(ctx, c, account, modelName, action, errorLog.Stream, body)
 		}
@@ -586,7 +586,7 @@ func (s *OpsService) executeWithAccount(ctx context.Context, reqType opsRetryReq
 			if s.antigravityGatewayService == nil {
 				return &opsRetryExecution{status: opsRetryStatusFailed, errorMessage: "antigravity gateway service not available"}
 			}
-			_, err = s.antigravityGatewayService.Forward(ctx, c, account, body)
+			_, err = s.antigravityGatewayService.Forward(ctx, c, account, body, false)
 		case PlatformGemini:
 			if s.geminiCompatService == nil {
 				return &opsRetryExecution{status: opsRetryStatusFailed, errorMessage: "gemini gateway service not available"}