**feat(auth, executor, cmd): add Antigravity provider integration**

- Implemented OAuth login flow for the Antigravity provider in `auth/antigravity.go`.
- Added `AntigravityExecutor` for handling requests and streaming via Antigravity APIs.
- Created `antigravity_login.go` command for triggering Antigravity authentication.
- Introduced OpenAI-to-Antigravity translation logic in `translator/antigravity/openai/chat-completions`.

**refactor(translator, executor): update Gemini CLI response translation and add Antigravity payload customization**

- Renamed Gemini CLI translation methods to align with response handling (`ConvertGeminiCliResponseToGemini` and `ConvertGeminiCliResponseToGeminiNonStream`).
- Updated `init.go` to reflect these method changes.
- Introduced `geminiToAntigravity` function to embed metadata (`model`, `userAgent`, `project`, etc.) into Antigravity payloads.
- Added random project, request, and session ID generators for enhanced tracking.
- Streamlined `buildRequest` to use `geminiToAntigravity` transformation before request execution.

internal/translator/gemini-cli/gemini/init.go

@@ -12,8 +12,8 @@ func init() {
 		GeminiCLI,
 		ConvertGeminiRequestToGeminiCLI,
 		interfaces.TranslateResponse{
-			Stream:     ConvertGeminiCliRequestToGemini,
-			NonStream:  ConvertGeminiCliRequestToGeminiNonStream,
+			Stream:     ConvertGeminiCliResponseToGemini,
+			NonStream:  ConvertGeminiCliResponseToGeminiNonStream,
 			TokenCount: GeminiTokenCount,
 		},
 	)