fix vibe engine audit findings: pg.Pool, plan replan, dead exclusions, legacy engine removal

Backend:
- app.ts: switch shared pg.Client to pg.Pool with per-transaction clients (#205)
- v2.routes.ts: replace plan instead of appending on replan, fixing self-duplication (#206)
- session-director: populate recentExclusions, per-candidate ranking, batch repetition checks (#209/#211/#213/#215 + minor)
- db.service.ts: claim-fusion watermark, legacy recommendation_batch engine removed (#216/#219/#232)
- app.ts: drop test enqueue-job endpoint (#234)

Frontend:
- AudioEngine/Vibe/usePlaybackStore: dedupe completed feedback, gate feedback to vibe sessions, End Vibe stops playback, Keep toast, shuffle played-set (#207/#236/#237/#238/#239/#240)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/pages/Vibe.tsx

@@ -9,6 +9,8 @@ import { TrackRow } from '../components/TrackRow';
 import { PageContainer } from '../components/PageContainer';
 import type { Track } from '../types';
 import { VibeTimeline } from '../components/VibeTimeline';
+import { suppressAutoFeedback } from '../components/AudioEngine';
+import { toast } from '../store/useToastStore';
 
 const INITIAL_BATCH_SIZE = 5;
 const PREFETCH_THRESHOLD = 3;
@@ -19,7 +21,7 @@ function bestEffort(p: Promise<unknown>): void {
 }
 
 export default function Vibe() {
-  const { currentTrack, queue, setQueue, playTrack, next: playNext } = usePlaybackStore();
+  const { currentTrack, queue, setQueue, playTrack, next: playNext, pause, setCurrentTrack } = usePlaybackStore();
   const {
     activeSessionId,
     buffer,
@@ -117,23 +119,34 @@ export default function Vibe() {
     if (idx > 0) {
       setBuffer(buffer.slice(idx));
     }
-  }, [activeSessionId, currentTrack]);
+  }, [activeSessionId, currentTrack, buffer, setBuffer]);
 
   const handleKeep = useCallback(() => {
-    if (currentTrack) bestEffort(vibeService.feedback(currentTrack.id, 'promoted'));
+    if (currentTrack) {
+      bestEffort(vibeService.feedback(currentTrack.id, 'promoted'));
+      toast.success(`Kept "${currentTrack.title}"`);
+    }
   }, [currentTrack]);
 
   const handleDislike = useCallback(() => {
-    if (currentTrack) bestEffort(vibeService.feedback(currentTrack.id, 'disliked'));
+    if (currentTrack) {
+      bestEffort(vibeService.feedback(currentTrack.id, 'disliked'));
+      // AudioEngine would otherwise also record a 'skipped' on the track
+      // change caused by playNext() below — suppress that duplicate.
+      suppressAutoFeedback(currentTrack.id);
+    }
     playNext();
   }, [currentTrack, playNext]);
 
   const handleEnd = useCallback(() => {
     // V2 plan expires via Redis TTL (2h). No explicit end endpoint.
+    pause();
+    setQueue([]);
+    setCurrentTrack(null);
     reset();
     setEmpty(false);
     setError(null);
-  }, [reset]);
+  }, [reset, pause, setQueue, setCurrentTrack]);
 
   const upcoming = currentTrack
     ? (() => {
@@ -208,12 +221,12 @@ export default function Vibe() {
           <div className="space-y-2">
             <h2 className="text-sm font-semibold text-muted">Or pick a seed track</h2>
             <ul className="max-h-72 space-y-1 overflow-y-auto">
-              {libraryTracks.map((track) => (
+              {libraryTracks.map((track, index) => (
                 <li key={track.id}>
                   <TrackRow
                     track={track}
                     queue={libraryTracks}
-                    index={libraryTracks.findIndex((t) => t.id === track.id)}
+                    index={index}
                     showActions={false}
                   />
                 </li>