feat: implement AI-curated playlist service and dashboard integration

- Added hierarchical AGENTS.md knowledge base
- Implemented PlaylistService with 6h themed and 24h devotion mix logic
- Integrated AI theme generation for 6h playlists via Gemini/OpenAI
- Added /playlists/refresh and metadata endpoints to API
- Updated background worker with scheduled playlist curation
- Created frontend PlaylistsSection, Tooltip components and integrated into Dashboard
- Added Alembic migration for playlist tracking columns
- Fixed Docker healthcheck with curl installation

backend/alembic/versions/5ed73db9bab9_add_playlist_columns.py

@@ -0,0 +1,45 @@
+"""add playlist columns
+
+Revision ID: 5ed73db9bab9
+Revises: b2c3d4e5f6g7
+Create Date: 2025-12-30 02:10:00.000000
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "5ed73db9bab9"
+down_revision = "b2c3d4e5f6g7"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column(
+        "analysis_snapshots", sa.Column("playlist_theme", sa.String(), nullable=True)
+    )
+    op.add_column(
+        "analysis_snapshots",
+        sa.Column("playlist_theme_reasoning", sa.Text(), nullable=True),
+    )
+    op.add_column(
+        "analysis_snapshots",
+        sa.Column("six_hour_playlist_id", sa.String(), nullable=True),
+    )
+    op.add_column(
+        "analysis_snapshots", sa.Column("daily_playlist_id", sa.String(), nullable=True)
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column("analysis_snapshots", "daily_playlist_id")
+    op.drop_column("analysis_snapshots", "six_hour_playlist_id")
+    op.drop_column("analysis_snapshots", "playlist_theme_reasoning")
+    op.drop_column("analysis_snapshots", "playlist_theme")
+    # ### end Alembic commands ###