Merge functional changes from develop branch:
- Remove AntigravityQuotaScope system (claude/gemini_text/gemini_image)
- Replace with per-model rate limiting using resolveAntigravityModelKey
- Remove model load statistics (IncrModelCallCount/GetModelLoadBatch)
- Simplify account selection to unified priority→load→LRU algorithm
- Remove SetAntigravityQuotaScopeLimit from AccountRepository
- Clean up scope-related UI indicators and API fields
- Change antigravitySmartRetryMaxAttempts from 3 to 1 to prevent
repeated rate limiting and long waits
- Clear sticky session binding (DeleteSessionAccountID) after smart
retry exhaustion, so subsequent requests don't hit the same
rate-limited account
- Add flow diagrams to Forward/ForwardGemini doc comments
- Add comprehensive unit tests covering:
- Sticky session cleared on retry failure (429, 503, network error)
- Sticky session NOT cleared on retry success
- Sticky session NOT cleared for non-sticky requests (empty hash)
- Sticky session NOT cleared on long delay path (handled by handler)
- Nil cache safety (no panic)
- MaxAttempts constant verification
- End-to-end retryLoop → switchError propagation with session clear
- GetAccessToken: add upstream branch to read api_key from credentials
- shouldTriggerAntigravitySmartRetry: relax check from IsOAuth to Platform-based
- isModelSupportedByAccount/WithContext: replace IsAntigravityModelSupported
whitelist with mapAntigravityModel for unified scheduling/forwarding logic
- mapAntigravityModel: fix edge case where wildcard target equals request model
- Update tests for new behavior and add custom model_mapping test cases
