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.

configure_fm350_5g.sh

@@ -29,10 +29,11 @@ log_error() { echo -e "${RED}[ERROR]${NC} $1"; }
 send_at_cmd() {
     local cmd="$1"
     local wait="${2:-2}"
-    
+    [ -c "$AT_PORT" ] || return 1
     cat $AT_PORT 2>/dev/null &
     local CAT_PID=$!
     sleep 0.3
+    [ -c "$AT_PORT" ] || { kill $CAT_PID 2>/dev/null; return 1; }
     echo -e "${cmd}\r" > $AT_PORT
     sleep $wait
     kill $CAT_PID 2>/dev/null || true
@@ -41,8 +42,9 @@ send_at_cmd() {
 get_at_response() {
     local cmd="$1"
     local wait="${2:-2}"
-    
+    [ -c "$AT_PORT" ] || return 1
     timeout $((wait + 3)) sh -c "
+        [ -c \"$AT_PORT\" ] || exit 1
         cat $AT_PORT 2>/dev/null &
         CAT_PID=\$!
         sleep 0.3