feat(mcp): implement unified MCP management for v3.7.0

BREAKING CHANGE: Migrate from app-specific MCP storage to unified structure

## Phase 1: Data Structure Migration
- Add McpApps struct with claude/codex/gemini boolean fields
- Add McpServer struct for unified server definition
- Add migration logic in MultiAppConfig::migrate_mcp_to_unified()
- Integrate automatic migration into MultiAppConfig::load()
- Support backward compatibility through Optional fields

## Phase 2: Backend Services Refactor
- Completely rewrite services/mcp.rs for unified management:
  * get_all_servers() - retrieve all MCP servers
  * upsert_server() - add/update unified server
  * delete_server() - remove server
  * toggle_app() - enable/disable server for specific app
  * sync_all_enabled() - sync to all live configs
- Add single-server sync functions to mcp.rs:
  * sync_single_server_to_claude/codex/gemini()
  * remove_server_from_claude/codex/gemini()
- Add read_mcp_servers_map() to claude_mcp.rs and gemini_mcp.rs
- Add new Tauri commands to commands/mcp.rs:
  * get_mcp_servers, upsert_mcp_server, delete_mcp_server
  * toggle_mcp_app, sync_all_mcp_servers
- Register new commands in lib.rs

## Migration Strategy
- Detects old structure (mcp.claude/codex/gemini.servers)
- Merges into unified mcp.servers with apps markers
- Handles conflicts by merging enabled apps
- Clears old structures after migration
- Saves migrated config automatically

## Known Issues
- Old commands still need compatibility layer (WIP)
- toml_edit type conversion needs fixing (WIP)
- Frontend not yet implemented (Phase 3 pending)

Related: v3.6.2 -> v3.7.0

src-tauri/src/lib.rs

@@ -18,14 +18,16 @@ mod settings;
 mod store;
 mod usage_script;
 
-pub use app_config::{AppType, MultiAppConfig};
+pub use app_config::{AppType, McpServer, MultiAppConfig};
 pub use codex_config::{get_codex_auth_path, get_codex_config_path, write_codex_live_atomic};
 pub use commands::*;
 pub use config::{get_claude_mcp_path, get_claude_settings_path, read_json_file};
 pub use error::AppError;
 pub use mcp::{
-    import_from_claude, import_from_codex, import_from_gemini, sync_enabled_to_claude,
-    sync_enabled_to_codex, sync_enabled_to_gemini,
+    import_from_claude, import_from_codex, import_from_gemini, remove_server_from_claude,
+    remove_server_from_codex, remove_server_from_gemini, sync_enabled_to_claude,
+    sync_enabled_to_codex, sync_enabled_to_gemini, sync_single_server_to_claude,
+    sync_single_server_to_codex, sync_single_server_to_gemini,
 };
 pub use provider::{Provider, ProviderMeta};
 pub use services::{
@@ -545,6 +547,12 @@ pub fn run() {
             commands::import_mcp_from_claude,
             commands::import_mcp_from_codex,
             commands::import_mcp_from_gemini,
+            // v3.7.0: Unified MCP management
+            commands::get_mcp_servers,
+            commands::upsert_mcp_server,
+            commands::delete_mcp_server,
+            commands::toggle_mcp_app,
+            commands::sync_all_mcp_servers,
             // Prompt management
             commands::get_prompts,
             commands::upsert_prompt,