feat(gemini): implement full MCP management functionality

- Add gemini_mcp.rs module for Gemini MCP file I/O operations
- Implement sync_enabled_to_gemini to export enabled MCPs to ~/.gemini/settings.json
- Implement import_from_gemini to import MCPs from Gemini config
- Add Gemini sync logic in services/mcp.rs (upsert_server, delete_server, set_enabled)
- Register Tauri commands for Gemini MCP sync and import
- Update frontend API calls and McpPanel to support Gemini

Fixes the issue where adding MCP servers in Gemini tab would not sync to ~/.gemini/settings.json

src/lib/api/mcp.ts

@@ -86,4 +86,12 @@ export const mcpApi = {
   async syncEnabledToCodex(): Promise<boolean> {
     return await invoke("sync_enabled_mcp_to_codex");
   },
+
+  async syncEnabledToGemini(): Promise<boolean> {
+    return await invoke("sync_enabled_mcp_to_gemini");
+  },
+
+  async importFromGemini(): Promise<number> {
+    return await invoke("import_mcp_from_gemini");
+  },
 };