Add interactive mod menu with GUI for all players

Features:
- Press F5 to open/close the mod menu
- Self options: health, armor, weapons, god mode, skins
- Vehicle spawner: 50+ vehicles organized by category
- Vehicle options: repair, flip, colors, drift mode, handling
- Network options: player list, teleport to other players
- Teleport locations: 15+ Liberty City locations
- World options: time and weather control
- Weapons menu: individual and all weapons
- Fun options: launch, ragdoll, ped spawning

Menu navigation via arrow keys, Enter to select, Backspace to go back

server.xml

@@ -33,5 +33,6 @@
         <resource src="chat" />
         <resource src="teleport" />
         <resource src="vehicles" />
+        <resource src="modmenu" />
     </resources>
 </server>