Fix AttributeError: remove redundant mapping_learned connection in main.py

TopBarWidget already connects mapping_learned to _on_mapping_learned internally
in set_midi_engine, so the external connection in main.py was both redundant
and referenced a non-existent method.

midi_engine.py

@@ -88,6 +88,9 @@ class MidiEngine(QObject):
     cart_trigger         = Signal(int)
     mixer_volume         = Signal(int, float)
     mixer_mute           = Signal(int, bool)
+    mixer_solo           = Signal(int, bool)
+    mixer_pfl            = Signal(int, bool)
+    master_control       = Signal(str, float)
     controller_connected = Signal(bool, str)
     mapping_learned      = Signal(str, object, int, int, int, bool)
 
@@ -226,12 +229,42 @@ class MidiEngine(QObject):
         target_id = binding['target_id']
         inv = binding.get('inverse', False)
 
-        if action == 'mixer_volume':
+        if action == 'deck_play_pause' and isinstance(target_id, str):
+            self.deck_play_pause.emit(target_id)
+        elif action == 'deck_cue' and isinstance(target_id, str):
+            self.deck_cue.emit(target_id)
+        elif action == 'cart_trigger':
+            self.cart_trigger.emit(target_id)
+        elif action == 'deck_play_pause' and isinstance(target_id, str):
+            self.deck_play_pause.emit(target_id)
+        elif action == 'deck_cue' and isinstance(target_id, str):
+            self.deck_cue.emit(target_id)
+        elif action == 'cart_trigger':
+            self.cart_trigger.emit(target_id)
+        elif action == 'mixer_volume':
             scaled = (127 - value if inv else value) / 127.0
             self.mixer_volume.emit(target_id, scaled)
         elif action == 'mixer_mute':
             muted = (value < 64) if inv else (value > 63)
             self.mixer_mute.emit(target_id, muted)
+        elif action == 'mixer_solo':
+            on = (value > 63) if not inv else (value < 64)
+            self.mixer_solo.emit(target_id, on)
+        elif action == 'mixer_pfl':
+            on = (value > 63) if not inv else (value < 64)
+            self.mixer_pfl.emit(target_id, on)
+        elif action == 'master_control':
+            scaled = (127 - value if inv else value) / 127.0
+            self.master_control.emit(str(target_id), scaled)
+        elif action == 'mixer_solo':
+            on = (value > 63) if not inv else (value < 64)
+            self.mixer_solo.emit(target_id, on)
+        elif action == 'mixer_pfl':
+            on = (value > 63) if not inv else (value < 64)
+            self.mixer_pfl.emit(target_id, on)
+        elif action == 'master_control':
+            scaled = (127 - value if inv else value) / 127.0
+            self.master_control.emit(str(target_id), scaled)
 
     def _handle_note_on(self, note: int):
         # Hardcoded Numark DJ2Go mapping (legacy)