Add YouTube Music playlist import support

- Add ytmusicapi dependency for fetching public YouTube Music playlists
- Create youtube_music service with playlist fetching and track search
- Add /api/youtube-music/import and /api/youtube-music/search endpoints
- Add importYouTubePlaylist and searchYouTubeMusic API client functions
- Update Playlists page with YouTube Music import button and URL input modal

frontend/src/lib/api.ts

@@ -156,4 +156,35 @@ export const getSavedRecommendations = () =>
 export const toggleSaveRecommendation = (id: string) =>
   api.post<{ saved: boolean }>(`/recommendations/${id}/toggle-save`).then((r) => r.data)
 
+// YouTube Music Import
+export interface YouTubeTrackResult {
+  title: string
+  artist: string
+  album: string | null
+  youtube_id: string | null
+  image_url: string | null
+}
+
+export const importYouTubePlaylist = (url: string) =>
+  api.post<PlaylistDetailResponse>('/youtube-music/import', { url }).then((r) => r.data)
+
+export const searchYouTubeMusic = (query: string) =>
+  api.post<YouTubeTrackResult[]>('/youtube-music/search', { query }).then((r) => r.data)
+
+// Billing
+export interface BillingStatusResponse {
+  is_pro: boolean
+  subscription_status: string | null
+  current_period_end: number | null
+}
+
+export const createCheckout = () =>
+  api.post<{ url: string }>('/billing/create-checkout').then((r) => r.data)
+
+export const createBillingPortal = () =>
+  api.post<{ url: string }>('/billing/portal').then((r) => r.data)
+
+export const getBillingStatus = () =>
+  api.get<BillingStatusResponse>('/billing/status').then((r) => r.data)
+
 export default api