Add 8-channel mixer with master compressor/limiter, MIDI learn system, separate deck outputs

- Mixer: 8 renamable stereo input channels with VU meter, volume fader, mute/solo
- Master bus: compressor (threshold, ratio, attack, release, makeup) + limiter (ceiling), LUFS metering
- Decks/carts keep their own JACK outputs, completely separate from mixer
- MIDI learn: configurable bindings saved to ~/.gti_radiostudio/midi_map.json
- mixer_widget.py: QDial-based DSP controls, scrollable channel strips

main.py

@@ -15,7 +15,7 @@ from playlist_widget import PlaylistWidget
 from midi_engine import MidiEngine
 from top_bar_widget import TopBarWidget, THEMES
 from history_widget import HistoryWidget
-from lufs_meter_widget import LUFSMeterWidget
+from mixer_widget import MixerWidget
 
 
 class RadioPanelWindow(QMainWindow):
@@ -70,29 +70,30 @@ class RadioPanelWindow(QMainWindow):
 
         self.history_widget = HistoryWidget()
 
-        self.lufs_meter = LUFSMeterWidget(self.engine)
+        self.mixer = MixerWidget(self.engine)
 
-        # ── Centre column ─────────────────────────────────────────────────
-        centre_col = QHBoxLayout()
+        # ── Centre column (decks + carts + mixer) ─────────────────────────
+        centre_col = QVBoxLayout()
         centre_col.setSpacing(8)
 
-        # Decks column
-        deck_col = QVBoxLayout()
-        deck_col.setSpacing(8)
+        # Top: decks row + carts
+        deck_area = QWidget()
+        deck_area.setStyleSheet("background: transparent; border: none;")
+        deck_layout = QVBoxLayout(deck_area)
+        deck_layout.setContentsMargins(0, 0, 0, 0)
+        deck_layout.setSpacing(8)
 
         deck_row = QHBoxLayout()
         deck_row.setSpacing(8)
         deck_row.addWidget(self.deck1)
         deck_row.addWidget(self.deck2)
-        deck_col.addLayout(deck_row)
+        deck_layout.addLayout(deck_row)
+        deck_layout.addWidget(self.cart_bank)
+        deck_layout.addStretch()
 
-        deck_col.addWidget(self.cart_bank)
-        deck_col.addStretch()
-
-        centre_col.addLayout(deck_col)
-
-        # LUFS meter on right of centre section
-        centre_col.addWidget(self.lufs_meter)
+        # Bottom: mixer
+        centre_col.addWidget(deck_area, stretch=1)
+        centre_col.addWidget(self.mixer)
 
         centre_widget = QWidget()
         centre_widget.setStyleSheet("background: transparent; border: none;")
@@ -138,6 +139,7 @@ class RadioPanelWindow(QMainWindow):
         self.deck2.apply_theme(theme)
         self.cart_bank.apply_theme(theme)
         self.history_widget.apply_theme(theme)
+        self.mixer.apply_theme(theme)
 
     def _apply_global_style(self, theme: dict):
         self.setStyleSheet(f"""
@@ -164,6 +166,8 @@ class RadioPanelWindow(QMainWindow):
         self.midi.deck_cue.connect(self._on_midi_cue)
         self.midi.deck_jog.connect(self._on_midi_jog)
         self.midi.cart_trigger.connect(self._on_midi_cart)
+        self.midi.mixer_volume.connect(self._on_midi_mixer_volume)
+        self.midi.mixer_mute.connect(self._on_midi_mixer_mute)
         self.midi.controller_connected.connect(self._on_midi_status)
 
         self.midi.start()
@@ -189,6 +193,12 @@ class RadioPanelWindow(QMainWindow):
     def _on_midi_cart(self, slot: int):
         self.cart_bank.slots[slot].toggle()
 
+    def _on_midi_mixer_volume(self, channel: int, value: float):
+        self.engine.set_channel_volume(channel, value)
+
+    def _on_midi_mixer_mute(self, channel: int, muted: bool):
+        self.engine.set_channel_mute(channel, muted)
+
     def _on_midi_status(self, connected: bool, name: str):
         if connected:
             print(f"[MIDI] Connected: {name}")
@@ -225,4 +235,4 @@ def main():
 
 
 if __name__ == "__main__":
-    main()
+    main()