Fix voltage monitor notifications and stability issues

Two critical fixes for the voltage monitoring system when 4G is active
on battery power:

1. Desktop Notifications Now Working:
   - Fixed D-Bus socket detection in voltage-alert-notify.sh
   - Changed from non-existent 'dbus-session' file to correct socket
     path /run/user/$USER_ID/bus
   - Notifications now properly appear when voltage drops below 3.45V
   - Added timestamp to notification message for better tracking
   - Made notification message more compact and actionable

2. Voltage Monitor Stability Fixed:
   - Added nohup when backgrounding monitor process in voltage-monitor-control.sh
   - Prevents SIGHUP signal when parent script exits
   - Monitor now remains stable and continuously detects low voltage
   - Rate-limited alerts working correctly (every 30 seconds)

Testing confirmed:
- Notifications display correctly with timestamp
- Monitor survives AC connect/disconnect cycles
- Low voltage detection working (threshold: 3.45V)
- Alerts sent successfully during battery drain with 4G active

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

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

scripts/voltage-alert-notify.sh

@@ -37,11 +37,12 @@ if command -v notify-send &> /dev/null; then
             export XDG_RUNTIME_DIR="/run/user/$USER_ID"
 
             # Send notification as the user
+            TIMESTAMP=$(date '+%H:%M:%S')
             sudo -u "#$USER_ID" DISPLAY=:0 DBUS_SESSION_BUS_ADDRESS="$DBUS_SESSION_BUS_ADDRESS" \
                 notify-send -u critical \
                 -i battery-caution \
                 "⚠️ Low Battery Voltage" \
-                "Battery at ${VOLTAGE}V\n4G module may hang!\n\nConsider:\n• Charge the battery\n• Disable 4G module\n• Reduce system load" \
+                "[${TIMESTAMP}] ${VOLTAGE}V - 4G module may hang!\nCharge battery or disable 4G." \
                 2>/dev/null &
 
             break

scripts/voltage-monitor-control.sh

@@ -58,8 +58,8 @@ start_monitor() {
         return 1
     fi
 
-    # Start the monitor in background
-    "$MONITOR_SCRIPT" &
+    # Start the monitor in background with nohup to prevent SIGHUP on parent exit
+    nohup "$MONITOR_SCRIPT" > /dev/null 2>&1 &
     MONITOR_PID=$!
 
     # Save PID