🐛 | Fix SonarQube issues

- Extract duplicated string literals into constants (S1192)
- Replace dict() with {} literal (S7498)
- Remove duplicate test_zero_ms (S4144)
- Remove/rename unused variables (S1481)
- Replace constant assert True with comment (S5914)
- Mark stub empty methods as intentional (S1186)
- Review 2 security hotspots as safe (S5443)

tests/test_music_db.py

@@ -24,14 +24,14 @@ def music_db():
 
 # ── Helper ────────────────────────────────────────────────────────────────────
 
-_SONG = dict(
-    video_id="test_video_001",
-    title="Test Song",
-    artists=[{"name": "Test Artist", "id": "artist_001"}],
-    album={"name": "Test Album", "id": "album_001"},
-    duration=240,
-    thumbnail="https://example.com/thumb.jpg",
-)
+_SONG = {
+    "video_id": "test_video_001",
+    "title": "Test Song",
+    "artists": [{"name": "Test Artist", "id": "artist_001"}],
+    "album": {"name": "Test Album", "id": "album_001"},
+    "duration": 240,
+    "thumbnail": "https://example.com/thumb.jpg",
+}
 
 
 def _record_play(db, **overrides):