- Add CORE_ROUTER_REGISTRY and OPTIONAL_ROUTER_REGISTRY for declarative router config
- Add profile gating via ALWRITY_ROUTER_PROFILE / ALWRITY_FEATURE_TO_ENABLE
- Only include routers whose profiles match active profile (podcast profile includes subscription, podcast)
- Use dynamic import_module for lazy loading
- Support include_kwargs for routers needing special args (youtube, research_config)
- Simplify include_core_routers and include_optional_routers to use registry
Reduces router_manager.py from 272 to ~156 lines.