Add vibe-contextual feedback system with dashboard observability

Adds feedback API endpoints that record up/down/skip signals tied to
vibe context (CLAP embeddings + text). Dashboard now shows Feedback
Activity (recent events with signal counts) and Vibe Influence (how
the same track gets rated differently across vibes).

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

alembic/versions/004_add_feedback_events.py

@@ -0,0 +1,44 @@
+"""Add feedback_events table and vibe_embedding to playlists
+
+Revision ID: 004
+Revises: 003
+Create Date: 2026-02-23
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from pgvector.sqlalchemy import Vector
+
+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:
+    # Add vibe_embedding to playlists (nullable — only set for vibe playlists)
+    op.add_column("playlists", sa.Column("vibe_embedding", Vector(512), nullable=True))
+
+    # Create feedback_events table
+    op.create_table(
+        "feedback_events",
+        sa.Column("id", sa.BigInteger, primary_key=True),
+        sa.Column("playlist_id", sa.BigInteger, sa.ForeignKey("playlists.id"), nullable=False),
+        sa.Column("track_id", sa.BigInteger, sa.ForeignKey("tracks.id"), nullable=False),
+        sa.Column("vibe_embedding", Vector(512), nullable=False),
+        sa.Column("vibe_text", sa.Text, nullable=True),
+        sa.Column("signal", sa.Text, nullable=False),
+        sa.Column("signal_weight", sa.REAL, nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+    )
+
+    # B-tree index on track_id (primary query pattern: fetch events by track)
+    op.create_index("ix_feedback_events_track_id", "feedback_events", ["track_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_feedback_events_track_id", table_name="feedback_events")
+    op.drop_table("feedback_events")
+    op.drop_column("playlists", "vibe_embedding")