🐛 | Improve test coverage for SonarQube quality gate

- Restructure conftest to try real Qt first, fall back to stubs
  only if that fails — ensures try/except guards in player.py and
  gui.py are exercised in CI, improving new_coverage
- Add tests for _migrate_legacy error paths (JSONDecodeError,
  OSError, db migration) — config.py now 100% covered
- Add tests for _disconnect, _send_presence exception handlers —
  discord_rpc.py now 97% covered
- Add tests for _cleanup_path and _tmp_dir helpers — player.py
  coverage bumped to 33%

tests/test_player_helpers.py

@@ -275,3 +275,69 @@ class TestBuildResolvedDict:
         assert resolved["duration"] == 99
         assert resolved["title"] == "Fallback"
         assert resolved["thumbnail"] == ""
+
+
+# ── _cleanup_path ───────────────────────────────────────────────────────────────
+
+class TestCleanupPath:
+    """Tests for DownloadWorker._cleanup_path."""
+
+    def _import(self):
+        from player import DownloadWorker
+        return DownloadWorker._cleanup_path
+
+    def test_removes_existing_file(self, tmp_path):
+        """_cleanup_path removes a file that exists."""
+        fn = self._import()
+        path = tmp_path / "to_delete.txt"
+        path.write_text("hello")
+        assert path.exists()
+        fn(str(path))
+        assert not path.exists()
+
+    def test_noop_for_missing_file(self):
+        """_cleanup_path does nothing for non-existent paths."""
+        fn = self._import()
+        fn("/nonexistent/path/file.txt")  # should not raise
+        assert True
+
+    def test_noop_for_none(self):
+        """_cleanup_path does nothing when path is None."""
+        fn = self._import()
+        fn(None)
+        assert True
+
+    def test_oserror_handled_gracefully(self, tmp_path, monkeypatch):
+        """_cleanup_path handles OSError gracefully."""
+        fn = self._import()
+        path = tmp_path / "locked.txt"
+        path.write_text("data")
+
+        def _fail_unlink(p):
+            raise OSError("Permission denied")
+
+        monkeypatch.setattr(os, "unlink", _fail_unlink)
+        fn(str(path))  # should not raise
+        assert True
+
+
+# ── _tmp_dir ───────────────────────────────────────────────────────────────────
+
+class TestTmpDir:
+    """Tests for the _tmp_dir helper."""
+
+    def _import(self):
+        from player import _tmp_dir
+        return _tmp_dir
+
+    def test_returns_string(self):
+        """_tmp_dir returns a string path."""
+        fn = self._import()
+        path = fn()
+        assert isinstance(path, str)
+        assert "tunetti" in path
+
+    def test_idempotent(self):
+        """Calling _tmp_dir multiple times returns the same path."""
+        fn = self._import()
+        assert fn() == fn()