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/bt_app.h

@@ -69,7 +69,7 @@ void bt_app_task_shut_down(void);
 void bt_app_init(void);
 
 /* Bluetooth device management for GUI */
-#define MAX_BT_DEVICES 20
+#define MAX_BT_DEVICES 8  // Reduced from 20 to save memory
 #define MAX_BT_NAME_LEN 32
 
 typedef struct {
@@ -100,6 +100,12 @@ bool bt_connect_device(int device_index);
 /* Clear discovered devices (keep paired devices) */
 void bt_clear_discovered_devices(void);
 
+/* Clear all devices from the device list (paired and discovered) */
+void bt_clear_all_devices(void);
+
+/* Disconnect from currently connected device */
+void bt_disconnect_current_device(void);
+
 /* Volume control functions */
 void bt_volume_up(void);
 void bt_volume_down(void);