feat(tray): add Gemini support to system tray menu (#209)

Refactor tray menu system to support three applications (Claude/Codex/Gemini):
- Introduce generic TrayAppSection structure and TRAY_SECTIONS array
- Implement append_provider_section and handle_provider_tray_event helper functions
- Enhance Gemini provider service with .env config read/write support
- Implement Gemini LiveSnapshot for atomic operations and rollback
- Update README documentation to reflect Gemini tray quick switching feature

README.md

@@ -47,7 +47,7 @@ Get 10% OFF the GLM CODING PLAN with [this link](https://z.ai/subscribe?ic=8JVLJ
 
 **Core Capabilities**
 
-- **Provider Management**: One-click switching between Claude Code & Codex API configurations
+- **Provider Management**: One-click switching between Claude Code, Codex, and Gemini API configurations
 - **MCP Integration**: Centralized MCP server management with stdio/http support and real-time sync
 - **Speed Testing**: Measure API endpoint latency with visual quality indicators
 - **Import/Export**: Backup and restore configs with auto-rotation (keep 10 most recent)
@@ -115,8 +115,8 @@ Download the latest `CC-Switch-v{version}-Linux.deb` package or `CC-Switch-v{ver
 2. **Switch Provider**:
    - Main UI: Select provider → Click "Enable"
    - System Tray: Click provider name directly (instant effect)
-3. **Takes Effect**: Restart terminal or Claude Code/Codex to apply changes
-4. **Back to Official**: Select "Official Login" preset, restart terminal, then use `/login` (Claude) or official login flow (Codex)
+3. **Takes Effect**: Restart your terminal or Claude Code / Codex / Gemini clients to apply changes
+4. **Back to Official**: Select the "Official Login" preset (Claude/Codex) or "Google Official" preset (Gemini), restart the corresponding client, then follow its login/OAuth flow
 
 ### MCP Management
 
@@ -139,6 +139,12 @@ Download the latest `CC-Switch-v{version}-Linux.deb` package or `CC-Switch-v{ver
 - API key field: `OPENAI_API_KEY` in `auth.json`
 - MCP servers: `~/.codex/config.toml` → `[mcp.servers]`
 
+**Gemini**
+
+- Live config: `~/.gemini/.env` (API key) + `~/.gemini/settings.json` (auth type for quick switching)
+- API key field: `GEMINI_API_KEY` inside `.env`
+- Tray quick switch: each provider switch rewrites `~/.gemini/.env` so the Gemini CLI picks up the new credentials immediately
+
 **CC Switch Storage**
 
 - Main config (SSOT): `~/.cc-switch/config.json`