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

backend/app/services/youtube_music.py

@@ -0,0 +1,87 @@
+import re
+
+from ytmusicapi import YTMusic
+
+ytmusic = YTMusic()
+
+
+def extract_playlist_id(url: str) -> str:
+    """Extract playlist ID from a YouTube Music playlist URL."""
+    match = re.search(r"[?&]list=([A-Za-z0-9_-]+)", url)
+    if not match:
+        raise ValueError("Invalid YouTube Music playlist URL")
+    return match.group(1)
+
+
+def get_playlist_tracks(playlist_url: str) -> tuple[str, str | None, list[dict]]:
+    """Fetch playlist info and tracks from a public YouTube Music playlist.
+
+    Returns (playlist_name, playlist_image_url, tracks).
+    Each track dict has: title, artist, album, youtube_id, image_url.
+    """
+    playlist_id = extract_playlist_id(playlist_url)
+    playlist = ytmusic.get_playlist(playlist_id, limit=None)
+
+    name = playlist.get("title", playlist_id)
+    image_url = None
+    thumbnails = playlist.get("thumbnails")
+    if thumbnails:
+        image_url = thumbnails[-1].get("url")
+
+    tracks = []
+    for item in playlist.get("tracks", []):
+        artists = item.get("artists") or []
+        artist_name = ", ".join(a.get("name", "") for a in artists if a.get("name"))
+
+        album_name = None
+        album = item.get("album")
+        if album:
+            album_name = album.get("name")
+
+        thumb_url = None
+        thumbs = item.get("thumbnails")
+        if thumbs:
+            thumb_url = thumbs[-1].get("url")
+
+        tracks.append({
+            "title": item.get("title", "Unknown"),
+            "artist": artist_name or "Unknown",
+            "album": album_name,
+            "youtube_id": item.get("videoId"),
+            "image_url": thumb_url,
+        })
+
+    return name, image_url, tracks
+
+
+def search_track(query: str) -> list[dict]:
+    """Search YouTube Music for tracks matching the query.
+
+    Returns a list of result dicts with: title, artist, album, youtube_id, image_url.
+    """
+    results = ytmusic.search(query, filter="songs", limit=10)
+
+    tracks = []
+    for item in results:
+        artists = item.get("artists") or []
+        artist_name = ", ".join(a.get("name", "") for a in artists if a.get("name"))
+
+        album_name = None
+        album = item.get("album")
+        if album:
+            album_name = album.get("name")
+
+        thumb_url = None
+        thumbs = item.get("thumbnails")
+        if thumbs:
+            thumb_url = thumbs[-1].get("url")
+
+        tracks.append({
+            "title": item.get("title", "Unknown"),
+            "artist": artist_name or "Unknown",
+            "album": album_name,
+            "youtube_id": item.get("videoId"),
+            "image_url": thumb_url,
+        })
+
+    return tracks