feat(api): add /api/requests user-facing CRUD

Implements POST/GET/GET:id/DELETE /api/requests handlers delegating to
lidarrrequests.Service; wires routes in RequireUser group and threads
the service through Mount and server.go.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/library_test.go

@@ -441,7 +441,7 @@ func TestRoutesRegisteredInMount(t *testing.T) {
 	r := chi.NewRouter()
 	w := playevents.NewWriter(h.pool, slog.New(slog.NewTextHandler(io.Discard, nil)),
 		30*time.Minute, 0.5, 30000)
-	Mount(r, h.pool, h.logger, w, config.RecommendationConfig{RadioSize: 50, RadioSizeMax: 200, RecentlyPlayedHours: 1}, h.lidarrCfg)
+	Mount(r, h.pool, h.logger, w, config.RecommendationConfig{RadioSize: 50, RadioSizeMax: 200, RecentlyPlayedHours: 1}, h.lidarrCfg, h.lidarrRequests)
 
 	paths := []string{
 		"/api/artists",