Root cause: Google's fetchAvailableModels API returns different model
catalogs depending on the endpoint. The daily endpoint returns 33
models including Gemini 3.8 Flash series, while the production
endpoint only returns 28 models without 3.8.
Additionally, the User-Agent header was using a stale Electron-style
format (Antigravity/4.3.0) that does not match the real Antigravity
client's UA (antigravity/hub/2.12.2), and unnecessary x-client-name /
x-client-version headers were being sent.
Changes:
- Reorder ANTIGRAVITY_ENDPOINTS to try daily endpoint first (matching
real Antigravity client behavior)
- Update ANTIGRAVITY_USER_AGENT to match the real Antigravity hub UA
- Remove unnecessary x-client-name/x-client-version headers
- Add Gemini 3.8 Flash (high/medium/low/tiered) to static model list
- Add gemini-3.8-flash passthrough in resolveAntigravityModel
nanoha