feat: implement multi-provider support in media library

- Introduced IProviderRegistry to manage multiple media providers.
- Updated AppState to use provider_registry instead of a single media_provider.
- Refactored library routes to support provider-specific queries for collections, series, genres, and items.
- Enhanced ProgrammingBlock to include provider_id for algorithmic and manual content types.
- Modified frontend components to allow selection of providers and updated API calls to include provider parameters.
- Adjusted hooks and types to accommodate provider-specific functionality.

k-tv-backend/api/src/dto.rs

@@ -42,10 +42,20 @@ pub struct TokenResponse {
     pub expires_in: u64,
 }
 
+/// Per-provider info returned by `GET /config`.
+#[derive(Debug, Serialize)]
+pub struct ProviderInfo {
+    pub id: String,
+    pub capabilities: domain::ProviderCapabilities,
+}
+
 /// System configuration response
 #[derive(Debug, Serialize)]
 pub struct ConfigResponse {
     pub allow_registration: bool,
+    /// All registered providers with their capabilities.
+    pub providers: Vec<ProviderInfo>,
+    /// Capabilities of the primary provider — kept for backward compatibility.
     pub provider_capabilities: domain::ProviderCapabilities,
 }