refactor(oauth): move Antigravity OAuth logic to dedicated module

- Moved src/gemini/oauth.ts to src/antigravity/oauth.ts.
- Updated all import paths in index.ts, src/plugin.ts, and src/plugin/types.ts.
- Removed the GoogleOAuthPlugin alias as it was redundant after the move.

Author: shekohex

index.ts

@@ -1,15 +1,14 @@
 export {
-  AntigravityOAuthPlugin,
-  GoogleOAuthPlugin
+  AntigravityOAuthPlugin
 } from "./src/plugin";
 
 export {
   authorizeAntigravity,
   exchangeAntigravity
-} from "./src/gemini/oauth";
+} from "./src/antigravity/oauth";
 
 export type {
   AntigravityAuthorization,
   AntigravityTokenExchangeResult
-} from "./src/gemini/oauth";
+} from "./src/antigravity/oauth";
 

src/gemini/oauth.ts src/antigravity/oauth.tssrc/gemini/oauth.ts renamed to src/antigravity/oauth.ts

@@ -1,6 +1,6 @@
+import type { AntigravityTokenExchangeResult } from "./antigravity/oauth";
+import { authorizeAntigravity, exchangeAntigravity } from "./antigravity/oauth";
 import { ANTIGRAVITY_PROVIDER_ID, ANTIGRAVITY_REDIRECT_URI } from "./constants";
-import type { AntigravityTokenExchangeResult } from "./gemini/oauth";
-import { authorizeAntigravity, exchangeAntigravity } from "./gemini/oauth";
 import { accessTokenExpired, isOAuthAuth } from "./plugin/auth";
 import { promptProjectId } from "./plugin/cli";
 import { startAntigravityDebugRequest } from "./plugin/debug";
@@ -243,8 +243,6 @@ export const AntigravityOAuthPlugin = async (
   },
 });
 
-export const GoogleOAuthPlugin = AntigravityOAuthPlugin;
-
 function toUrlString(value: RequestInfo): string {
   if (typeof value === "string") {
     return value;

src/plugin.ts

@@ -1,5 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin";
-import type { AntigravityTokenExchangeResult } from "../gemini/oauth";
+import type { AntigravityTokenExchangeResult } from "../antigravity/oauth";
 
 export interface OAuthAuthDetails {
   type: "oauth";