chore: final fixes from post-refactor smoke test

artist_gallery redirect and reapply_artist_tags_from_paths both still
built f"artist:{name}" strings. Last stragglers cleaned up; the
dead-code sweep now returns zero prefix-construction hits.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/main.py

@@ -602,8 +602,11 @@ def artist_list():
 
 @main.route('/artist/<artist_name>')
 def artist_gallery(artist_name):
-    # Backward-compatible: go to gallery filtered by artist tag
-    return redirect(url_for('main.gallery', tag=f"artist:{artist_name}"))
+    # Backward-compatible: resolve artist to its tag id and redirect to the id-keyed gallery URL.
+    tag = Tag.query.filter_by(kind='artist', name=artist_name).first()
+    if tag is None:
+        return redirect(url_for('main.tag_list', kind='artist'))
+    return redirect(url_for('main.gallery', tag_id=tag.id))
 
 
 @main.route('/settings')
@@ -2038,10 +2041,9 @@ def reapply_artist_tags_from_paths():
                 continue
 
             # Create or get the artist tag
-            tag_name = f"artist:{artist_name}"
-            tag = Tag.query.filter_by(name=tag_name).first()
+            tag = Tag.query.filter_by(kind='artist', name=artist_name).first()
             if not tag:
-                tag = Tag(name=tag_name, kind='artist')
+                tag = Tag(kind='artist', name=artist_name)
                 db.session.add(tag)
                 db.session.flush()