v0.5 — cleanup orphan code, add MIDI master volume learn, fix turn-deck crashes

- Remove vestigial lufs_meter_widget.py and debug_audio.py
- Delete unused WaveformWidget/WaveformMonitor classes, dead stubs, duplicate code
- Fix turn-mode deck crashes (deck3/deck4 missing from engine.decks, uninitialized manual_elapsed/duration)
- Replace raw print() with logging in main.py
- Add master_volume MIDI learn signal + settings popup entry
- Bump version to 0.5

playlist_widget.py

@@ -6,15 +6,13 @@ from PySide6.QtWidgets import (
     QListWidget, QListWidgetItem, QAbstractItemView,
     QMenu, QSplitter
 )
-from PySide6.QtCore import Qt, QTimer, QSize, QSize
+from PySide6.QtCore import Qt, QTimer, QSize
 from PySide6.QtGui import QFont, QColor, QAction
 import json
 import os
 
 from icons import icon_save, icon_load
 
-from icons import icon_save, icon_load
-
 
 # ─────────────────────────────────────────
 # PLAYLIST ITEM
@@ -277,8 +275,7 @@ class BasePlaylistPanel(QWidget):
                 paths.append(item.filepath)
         return paths
 
-    def clear_list(self, lst: QListWidget):
-        lst.clear()
+    
 
 
 # ─────────────────────────────────────────