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/tests/import_export_sync.rs

@@ -553,6 +553,7 @@ command = "echo"
                 claude: false,
                 codex: false, // 初始未启用
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -680,6 +681,7 @@ fn import_from_claude_merges_into_config() {
                 claude: false, // 初始未启用
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,