presentation: HTTP server crate w/ handlers, routes, background tasks

Axum binary that wires all clean-arch crates together:
- AppState holds pre-built Deps structs (auth, channels, schedule, library, etc.)
- JWT extractors (CurrentUser, AdminUser, OptionalCurrentUser)
- Handlers delegate to application use cases, map to api-types DTOs
- Routes: auth, channels, schedule, library, admin, providers, config, iptv
- Background: auto-scheduler, broadcast poller, webhook consumer, library sync
- Factory builds everything from Config + DbPool
- SimpleProviderRegistry impl of IProviderRegistry trait
- NoopMediaProvider fallback

crates/presentation/src/mappers/mod.rs

@@ -0,0 +1,6 @@
+//! Domain → DTO mappings.
+//!
+//! Most conversions are already handled by `From` impls in the `api-types` crate.
+//! This module is reserved for any presentation-layer-specific mappings that
+//! don't belong in `api-types` (e.g., combining multiple domain objects into a
+//! single response).