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

README

@@ -8,7 +8,7 @@ VIBE CODED AS FUCK. DO WHAT YOU WANT. I DON'T OWN IT YOU DON'T
 | **Playlist Manager** | ✅ | Drag/drop, Add files/folder, Load to deck, Queue, Right-click menu |
 | **CART Playlist** | ✅ | Separate playlist panel, auto-fills next free cart slot |
 | **MIDI Controller** | ✅ | Numark DJ2Go - Play/Pause, Cue, Jog wheels, 4 Cart buttons |
-| **Audio Fingerprinting** | ⚠️ | AcoustID integrated, API working but database gaps |
+
 | **Play History** | ✅ | Scrollable session history, file tags + MusicBrainz metadata |
 | **Top Bar** | ✅ | 24hr clock, full date display |
 | **Colour Themes** | ✅ | 4 themes - Green, Amber, Blue, Red - cycle with ◈ button |
@@ -20,7 +20,6 @@ radiopanel/
 ├── deck_widget.py          # CDJ-style deck UI + transport controls
 ├── cart_widget.py          # 4-slot CART machine
 ├── playlist_widget.py      # Playlist + CART playlist panels
-├── fingerprint_widget.py   # AcoustID audio fingerprinting
 ├── midi_engine.py          # Numark DJ2Go MIDI mapping
 ├── top_bar_widget.py       # Clock, date, theme switcher
 ├── history_widget.py       # Session play history