v2.3.2: add Google Gemini provider with OAuth support

- Two presets: API Key and OAuth modes
- OAuth Login button: full Google OAuth2 flow with auto-refresh
- Auto-refreshes expired access tokens using refresh_token
- Gemini OpenAI-compatible endpoint works with existing proxy
- Models: gemini-2.5-flash, gemini-2.5-pro, gemini-2.0-flash, etc.

CHANGELOG.md

@@ -1,5 +1,18 @@
 # Changelog
 
+## v2.3.2 (2026-05-20)
+
+- **Added Google Gemini provider with OAuth support**
+  - Two presets: "Google Gemini (API Key)" and "Google Gemini (OAuth)"
+  - OAuth Login button in endpoint editor — full Google OAuth2 flow
+  - Starts local HTTP server (port 8085), opens browser for Google consent
+  - Captures auth code, exchanges for access + refresh tokens
+  - Stores tokens in `~/.cache/codex-proxy/google-oauth-token.json`
+  - Auto-refreshes access tokens when expired (no manual re-login)
+  - Uses Gemini's OpenAI-compatible endpoint: `generativelanguage.googleapis.com/v1beta/openai`
+  - Models: gemini-2.5-flash, gemini-2.5-pro, gemini-2.0-flash, gemini-2.0-flash-lite, and more
+  - Setup instructions shown if `client_secret.json` not found
+
 ## v2.3.0 (2026-05-20)
 
 - **Adaptive Crof self-healing system**