Previously, only Codex provider switches triggered MCP synchronization,
which could cause MCP configuration loss when switching Claude or Gemini
providers.
Changes:
- Enable MCP sync for all app types (Claude, Codex, Gemini) during provider switch
- Migrate to v3.7.0 unified MCP sync mechanism using McpService::sync_all_enabled()
- Replace app-specific sync_enabled_to_codex() with unified sync for all apps
- Remove unused mcp module import
This ensures MCP servers remain properly configured across all applications
after provider switches, preventing configuration loss.