Introduce a comprehensive settings management system that allows runtime
configuration through a new admin interface. The system includes:
- Database-backed settings with Redis caching for performance
- Settings registry defining types, defaults, and categories
- New admin UI with navigation cards and dedicated sub-pages for each category
(general, cache, indexers, proxy, system, TMDB)
- Shared view logic for consistent GET/POST handling across sub-pages
- Automatic seeding of defaults and application of overrides at startup
- Validation and type coercion for setting values
The previous static configuration page has been replaced with a modular,
category-based interface that provides better organization and extensibility
for future configuration needs.
