Fix Bluetooth pairing, menu crashes, and improve UX

Major fixes and improvements to Bluetooth device management and menu navigation:

**Bluetooth Device Pairing**
- Fixed discovered devices not being saved as paired after connection
- Only save devices to NVS when successfully connected (not just discovered)
- Auto-pair discovered devices on successful A2DP connection
- Update device list to show paired status immediately after connection

**Critical Bug Fixes**
- Fixed dangling pointer crash in NVS request/response mechanism
  - Was sending pointer to stack variable, now sends result value directly
  - Prevents crash when connecting to Bluetooth devices
- Fixed use-after-free crash when clicking menu items after dynamic updates
  - Menu context now properly synchronized after adding/removing items
  - Prevents InstructionFetchError crashes in menu navigation
- Fixed memory exhaustion by reducing MAX_BT_DEVICES from 20 to 8
  - Prevents heap allocation failures when populating device list

**Menu & UX Improvements**
- "Clear Paired" button now properly disconnects active connections
- "Clear Paired" button always visible when paired devices exist
- GUI updates immediately after clearing paired devices
- Paired devices marked with asterisk prefix (* Device Name)
- Removed redundant "(paired)" suffix text
- Long device names scroll smoothly when selected (3-second animation)
- Refresh button preserved during menu updates to prevent crashes
- Menu focus state properly maintained across all dynamic updates

**Technical Details**
- bt_add_discovered_device() no longer saves to NVS
- Added currentFocusIndex() calls after all menu modifications
- Improved clear_bt_device_list() to avoid deleting active buttons
- Added bt_disconnect_current_device() for clean disconnections
- Fixed NVS notification mechanism to avoid stack variable pointers

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

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

main/system.h

@@ -47,11 +47,14 @@ typedef struct SystemState_s
 
     // BT event data
     int btDeviceIndex;
-    
+
     // NVS cached data
     paired_device_t pairedDevices[MAX_PAIRED_DEVICES];
     size_t pairedDeviceCount;
 
+    // Charge status
+    bool isCharging;
+
 } SystemState_t;
 
 
@@ -67,6 +70,7 @@ typedef struct SystemState_s
 #define EM_EVENT_BT_CONNECT (1UL<<3)
 #define EM_EVENT_VOLUME_UP  (1UL<<4)
 #define EM_EVENT_VOLUME_DOWN (1UL<<5)
+#define EM_EVENT_BT_DISCOVERY_COMPLETE (1UL<<6)
 // …add more event bit-masks here…
 
 typedef struct {
@@ -83,6 +87,9 @@ ImuData_t system_getImuData(void);
 int system_getPrimaryAxis(void);
 float system_getAngle(void);
 
+void system_setChargeStatus(bool charging);
+bool system_getChargeStatus(void);
+
 void system_setZeroAngle(void);
 void system_clearZeroAngle(void);
 float system_getZeroAngle(void);
@@ -133,6 +140,7 @@ bool system_isDeviceKnown(esp_bd_addr_t bda);
 esp_err_t system_getKnownDeviceCount(size_t *count);
 esp_err_t system_updateConnectionTimestamp(esp_bd_addr_t bda);
 const paired_device_t* system_getPairedDevices(size_t *count);
+esp_err_t system_clearAllPairedDevices(void);
 
 
 #define NVS_TIMEOUT_MS 5000