feat(opencode): complete Phase 4 - MCP sync module

Add mcp/opencode.rs with format conversion between CC Switch and OpenCode:
- stdio ↔ local type conversion
- command+args ↔ command array format
- env ↔ environment field mapping
- sse/http ↔ remote type conversion

Public API:
- sync_enabled_to_opencode: Batch sync all enabled servers
- sync_single_server_to_opencode: Sync individual server
- remove_server_from_opencode: Remove from live config
- import_from_opencode: Import servers from OpenCode config

Also fix test files to include new opencode field in McpApps struct.
All 4 unit tests pass for format conversion.

src-tauri/src/mcp/mod.rs

@@ -8,10 +8,12 @@
 //! - `claude` - Claude MCP 同步和导入
 //! - `codex` - Codex MCP 同步和导入（含 TOML 转换）
 //! - `gemini` - Gemini MCP 同步和导入
+//! - `opencode` - OpenCode MCP 同步和导入（含 local/remote 格式转换）
 
 mod claude;
 mod codex;
 mod gemini;
+mod opencode;
 mod validation;
 
 // 重新导出公共 API
@@ -26,3 +28,7 @@ pub use gemini::{
     import_from_gemini, remove_server_from_gemini, sync_enabled_to_gemini,
     sync_single_server_to_gemini,
 };
+pub use opencode::{
+    import_from_opencode, remove_server_from_opencode, sync_enabled_to_opencode,
+    sync_single_server_to_opencode,
+};