refactor: remove /v1/gemini endpoint, replaced by /v1beta routes

- Delete handle_gemini handler (identical to handle_gemini_v1beta)
- Remove /v1/gemini route from router
- Update root handler service name to zerogravity
- Clean all doc references

src/api/mod.rs

@@ -48,7 +48,6 @@ pub fn router(state: Arc<AppState>) -> Router {
             "/v1/chat/completions",
             post(completions::handle_completions),
         )
-        .route("/v1/gemini", post(gemini::handle_gemini))
         .route(
             "/v1beta/{*path}",
             post(gemini::handle_gemini_v1beta),
@@ -72,7 +71,7 @@ pub fn router(state: Arc<AppState>) -> Router {
 
 async fn handle_root() -> Json<serde_json::Value> {
     Json(serde_json::json!({
-        "service": "antigravity-openai-proxy",
+        "service": "zerogravity",
         "version": "3.3.0",
         "runtime": "rust",
         "endpoints": [