🐛 | Fix SonarQube issues across codebase

- Add docstrings to all empty Qt stub methods (S1186)
- Fix BLOCKER S1845: rename playbackState to get_playback_state
- Rename enum fields to snake_case with CamelCase aliases (S116)
- Rename stub methods to snake_case (set_source, set_position, etc.) (S100)
- Rename unused timeout param to msecs (S1172)
- Remove unused state variables in tests (S1481)
- Replace 'is' with '==' for enum comparisons (S5795)
- Remove unnecessary list() calls (S7504)
- Rename QTh to qt_cls (S117)
- Remove commented-out code blocks (S125)
- Add docstring to FallbackServiceInterface.emit_properties_changed (S1186)

tests/test_import_fallbacks.py

@@ -27,7 +27,7 @@ import pytest
 def _clean_pyside_modules():
     """Remove PySide6 and target modules from sys.modules."""
     keys_to_del = []
-    for key in list(sys.modules.keys()):
+    for key in sys.modules:
         if key.startswith("PySide6") or key in ("player", "gui", "discord_rpc"):
             keys_to_del.append(key)
     for key in keys_to_del:
@@ -73,7 +73,7 @@ class TestPlayerQtFallback:
         sys.modules.pop("player", None)
         # PySide6 modules may have been removed, restore them by clearing
         # the cached import so that a fresh import re-imports the real lib.
-        for key in list(sys.modules.keys()):
+        for key in sys.modules:
             if key.startswith("PySide6") and key not in _ORIGINAL_PYSIDE_MODS:
                 del sys.modules[key]
 
@@ -145,8 +145,8 @@ class TestPlayerQtFallback:
             assert callable(player.QThread.quit)
             assert callable(player.QThread.wait)
             # Quick functional check
-            QTh = player.QThread
-            inst = QTh()
+            qt_cls = player.QThread
+            inst = qt_cls()
             inst.start()  # should not raise
             inst.quit()   # should not raise
             assert inst.wait() is True
@@ -212,7 +212,7 @@ class TestGuiQtFallback:
         """Remove stale fallback modules so subsequent tests get the real ones."""
         for mod_name in ("gui", "player", "discord_rpc"):
             sys.modules.pop(mod_name, None)
-        for key in list(sys.modules.keys()):
+        for key in sys.modules:
             if key.startswith("PySide6") and key not in _ORIGINAL_PYSIDE_MODS:
                 del sys.modules[key]