fix: add category parent menus for SecuBox modules

Added missing category parent menu entries that other SecuBox modules
depend on:
- admin/secubox/security (Security & Monitoring)
- admin/secubox/network (Network Management)
- admin/secubox/system (System & Performance)

Without these parent menus, individual modules like crowdsec, network-modes,
and system-hub couldn't register their menu entries under admin/secubox/*/

This allows all SecuBox modules to appear in the LuCI menu hierarchy.

Fixes: luci-app-secubox menu structure

luci-app-secubox/root/usr/share/luci/menu.d/luci-app-secubox.json

@@ -13,5 +13,20 @@
         "title": "Modules",
         "order": 20,
         "action": {"type": "view", "path": "secubox/modules"}
+    },
+    "admin/secubox/security": {
+        "title": "Security & Monitoring",
+        "order": 30,
+        "action": {"type": "firstchild"}
+    },
+    "admin/secubox/network": {
+        "title": "Network Management",
+        "order": 40,
+        "action": {"type": "firstchild"}
+    },
+    "admin/secubox/system": {
+        "title": "System & Performance",
+        "order": 50,
+        "action": {"type": "firstchild"}
     }
 }