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

frontend/src/types/index.ts

@@ -561,7 +561,10 @@ export interface Account {
   platform: AccountPlatform
   type: AccountType
   credentials?: Record<string, unknown>
-  extra?: CodexUsageSnapshot & Record<string, unknown> // Extra fields including Codex usage
+  // Extra fields including Codex usage and model-level rate limits (Antigravity smart retry)
+  extra?: (CodexUsageSnapshot & {
+    model_rate_limits?: Record<string, { rate_limited_at: string; rate_limit_reset_at: string }>
+  } & Record<string, unknown>)
   proxy_id: number | null
   concurrency: number
   current_concurrency?: number // Real-time concurrency count from Redis