refactor: extract interactive menus into dedicated index scripts

- move apps menu from inline lxs.sh function to apps/index.sh
- add tools/index.sh as entry point for tools menu
- rename system-tools.sh to system-infos.sh
- simplify help text to point users to the interactive menu
- update README directory tree to reflect new structure

README.md

@@ -60,13 +60,15 @@ lxs/
 ├── lib/
 │   └── common.sh          # Shared helpers (colors, loggers, spinner)
 ├── apps/                  # Application installers
+│   ├── index.sh           # Interactive menu listing the apps below
 │   ├── coolify.sh
 │   ├── pterodactyl.sh
 │   ├── uptime-kuma.sh
 │   ├── cloudpanel.sh
 │   └── proxmox.sh
 └── tools/                 # System tools
-    ├── system-tools.sh
+    ├── index.sh           # Interactive menu listing the tools below
+    ├── system-infos.sh
     ├── server-benchmark.sh
     └── harden.sh
 ```