Add delete button to taste profile tags in Stats

- Backend: DELETE /stats/taste/{tag} removes the row from user_tag_affinity
- API: deleteTasteTag(tag) helper
- Stats UI: × button on each tag chip, faint by default, full opacity on hover;
  invalidates stats query so the tag disappears immediately

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

frontend/src/pages/Stats.jsx

@@ -1,5 +1,5 @@
-import { useQuery } from "@tanstack/react-query";
-import { getStats } from "../api";
+import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { getStats, deleteTasteTag } from "../api";
 import { Link } from "react-router-dom";
 
 function fmt(seconds) {
@@ -22,12 +22,18 @@ function StatCard({ label, value, sub }) {
 }
 
 export default function Stats() {
+  const qc = useQueryClient();
   const { data, isLoading } = useQuery({
     queryKey: ["stats"],
     queryFn: () => getStats().then(r => r.data),
     staleTime: 5 * 60_000,
   });
 
+  const deleteTag = useMutation({
+    mutationFn: (tag) => deleteTasteTag(tag),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["stats"] }),
+  });
+
   if (isLoading) {
     return (
       <div className="flex items-center justify-center py-24">
@@ -178,7 +184,7 @@ export default function Stats() {
                 <span
                   key={t.tag}
                   title={`score: ${t.score.toFixed(1)}`}
-                  className="px-3 py-1 rounded-full text-xs font-medium"
+                  className="flex items-center gap-1 px-3 py-1 rounded-full text-xs font-medium"
                   style={{
                     backgroundColor: `rgba(250,204,21,${0.08 + intensity * 0.18})`,
                     color: `hsl(50,95%,${55 + intensity * 20}%)`,
@@ -186,6 +192,14 @@ export default function Stats() {
                   }}
                 >
                   {t.tag}
+                  <button
+                    onClick={() => deleteTag.mutate(t.tag)}
+                    disabled={deleteTag.isPending}
+                    className="opacity-40 hover:opacity-100 transition-opacity leading-none ml-0.5"
+                    title="Remove from taste profile"
+                  >
+                    ×
+                  </button>
                 </span>
               );
             })}