Add Bandcamp/YouTube links on all recs, Fix My Playlist, configurable rec count

- Bandcamp: match artist+song, fall back to artist-only page
- YouTube fallback: if not on Bandcamp, link to YouTube music video search
- Fix My Playlist: AI analyzes playlist, finds outliers, suggests replacements
- User chooses recommendation count (5, 10, 15, 20)

backend/alembic/versions/004_add_youtube_url.py

@@ -0,0 +1,24 @@
+"""Add youtube_url to recommendations
+
+Revision ID: 004
+Revises: 003
+Create Date: 2026-03-30
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "004"
+down_revision: Union[str, None] = "003"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("recommendations", sa.Column("youtube_url", sa.String(500), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("recommendations", "youtube_url")