Enhance Bluetooth functionality and GUI integration

- Add Bluetooth device list management with discovery and pairing support
- Implement volume control with AVRC integration
- Add system event handling for GUI-to-Bluetooth communication
- Enhance menu system with device selection and volume control pages
- Improve memory management by making menu creation lazy
- Add proper event subscription between GUI and Bluetooth modules
- Update filter coefficient for improved audio clicking behavior

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

main/system.h

@@ -32,10 +32,13 @@ typedef struct SystemState_s
     float zeroAngle;
     int primaryAxis;
 
+    // BT event data
+    int btDeviceIndex;
+
 } SystemState_t;
 
 
-#define MAX_INDICATION_ANGLE    5.0f
+#define MAX_INDICATION_ANGLE    7.5f
 #define FILTER_COEFF            0.4f        // 0 to 1   Smaller number is heavier filter
 #define PRIMARY_AXIS            ANGLE_YZ
 #define RIFLE_AXIS              Y
@@ -43,6 +46,10 @@ typedef struct SystemState_s
 #define EM_MAX_SUBSCRIBERS 8    // tweak as needed
 #define EM_EVENT_NEW_DATA   (1UL<<0)
 #define EM_EVENT_ERROR      (1UL<<1)
+#define EM_EVENT_BT_REFRESH (1UL<<2)
+#define EM_EVENT_BT_CONNECT (1UL<<3)
+#define EM_EVENT_VOLUME_UP  (1UL<<4)
+#define EM_EVENT_VOLUME_DOWN (1UL<<5)
 // …add more event bit-masks here…
 
 typedef struct {
@@ -72,5 +79,14 @@ BaseType_t system_unsubscribe(TaskHandle_t task);
 // Notify all subscribers of one or more event bits
 void    system_notifyAll(uint32_t eventBits);
 
+// BT-specific event functions
+void system_requestBtRefresh(void);
+void system_requestBtConnect(int device_index);
+int system_getBtDeviceIndex(void);
+
+// Volume control functions
+void system_requestVolumeUp(void);
+void system_requestVolumeDown(void);
+
 
 #endif