New capability interfaces:
- menus.Menus: menu/nav access (GetMenuByName, GetMenuItems)
- subscriptions.Subscriptions: tier/plan access (GetUserTierLevel, GetTierBySlug, ListActivePlans)
- auth.PublicUsers: public user profiles (GetByUsername, GetByID)
- plugin.PluginBridge: inter-plugin service registry with typed GetServiceAs[T] helper
All added to ServiceDeps for plugin consumption.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
