Enhance 5G modem management with integrated web GUI and connection control

- Introduced a web GUI for managing 5G connections, replacing the standalone 5g-router service.
- Updated scripts to ensure exclusive access to the AT port, preventing conflicts.
- Improved troubleshooting documentation in 5G_MODEM_TROUBLESHOOTING.md, adding checks for processes using the AT port.
- Enhanced connection management in the web app, including auto-connect and detailed status APIs.
- Updated installation scripts to reflect changes in service management and dependencies.

scripts/modem-status-at.sh

@@ -1,16 +1,22 @@
 #!/bin/sh
 # Alpine 5G Router – modem status via AT commands (AT_COMMANDS_REFERENCE.md)
 # Outputs JSON. Used by Web GUI /api/status.
-# Rev: 2  (see REVISION in repo root)
+# Rev: 3  (see REVISION in repo root)
 
 CONFIG="/etc/5g-router.conf"
 AT_PORT="${AT_PORT:-/dev/ttyUSB1}"
-[ -f "$CONFIG" ] && . "$CONFIG"
+AT_LOCK="/var/lock/5g-at.lock"
+[ -f "$CONFIG" ] && . "$CONFIG" || true
+
+# Acquire exclusive lock on AT port to avoid conflicts with connect-5g.sh
+exec 9>"$AT_LOCK"
+flock -w 10 9 || { echo '{"error":"AT port busy"}'; exit 1; }
 
 get_at() {
     _cmd="$1"
     _wait="${2:-1}"
     timeout $((_wait + 2)) sh -c "
+        [ -c \"$AT_PORT\" ] || exit 1
         cat $AT_PORT 2>/dev/null &
         _p=\$!
         sleep 0.3