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/env.py

@@ -10,6 +10,7 @@ from haunt_fm.models.base import Base
 
 # Import all models so they register with Base.metadata
 from haunt_fm.models.track import (  # noqa: F401
+    FeedbackEvent,
     ListenEvent,
     Playlist,
     PlaylistTrack,