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/mcp_commands.rs

@@ -214,6 +214,7 @@ fn set_mcp_enabled_for_codex_writes_live_config() {
                 claude: false,
                 codex: false, // 初始未启用
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -277,6 +278,7 @@ fn enabling_codex_mcp_skips_when_codex_dir_missing() {
                 claude: false,
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -320,6 +322,7 @@ fn upsert_mcp_server_disabling_app_removes_from_claude_live_config() {
                 claude: true,
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -352,6 +355,7 @@ fn upsert_mcp_server_disabling_app_removes_from_claude_live_config() {
                 claude: false,
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -483,6 +487,7 @@ fn enabling_gemini_mcp_skips_when_gemini_dir_missing() {
                 claude: false,
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,
@@ -536,6 +541,7 @@ fn enabling_claude_mcp_skips_when_claude_config_absent() {
                 claude: false,
                 codex: false,
                 gemini: false,
+                opencode: false,
             },
             description: None,
             homepage: None,