Add vibe-aware playlists with CLAP text embeddings

Blend taste profile with text-embedded mood descriptions (e.g. "chill
ambient lo-fi") using pre-blended vector search against the existing
HNSW index. New optional `vibe` and `alpha` params on playlist generate
and recommendations endpoints. Backward compatible — no vibe = pure
taste profile (alpha=1.0).

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

src/haunt_fm/api/playlists.py

@@ -1,5 +1,5 @@
 from fastapi import APIRouter, Depends
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -17,15 +17,31 @@ class GenerateRequest(BaseModel):
     name: str | None = None
     speaker_entity: str | None = None
     auto_play: bool = False
+    vibe: str | None = None
+    alpha: float = Field(default=0.5, ge=0.0, le=1.0)
 
 
 @router.post("/generate")
 async def generate(req: GenerateRequest, session: AsyncSession = Depends(get_session)):
+    # Compute text embedding for vibe description
+    vibe_embedding = None
+    if req.vibe:
+        from haunt_fm.services.embedding import embed_text, is_model_loaded, load_model
+
+        if not is_model_loaded():
+            load_model()
+        vibe_embedding = embed_text(req.vibe)
+    # Force pure taste when no vibe provided (preserves current behavior)
+    alpha = req.alpha if req.vibe else 1.0
+
     playlist = await generate_playlist(
         session,
         total_tracks=req.total_tracks,
         known_pct=req.known_pct,
         name=req.name,
+        vibe_embedding=vibe_embedding,
+        alpha=alpha,
+        vibe_text=req.vibe,
     )
 
     # Load playlist tracks with track info
@@ -58,6 +74,8 @@ async def generate(req: GenerateRequest, session: AsyncSession = Depends(get_ses
         "name": playlist.name,
         "total_tracks": playlist.total_tracks,
         "known_pct": playlist.known_pct,
+        "vibe": playlist.vibe,
+        "alpha": playlist.alpha,
         "tracks": track_list,
         "auto_played": req.auto_play and req.speaker_entity is not None,
     }