Fix headless class_name dependencies

- Replaced TeamData.Team type hints with int in all scripts
- Added explicit preloads for headless mode class resolution
- Created stub LagCompensation and DamageProcessor scripts
- Fixed PluginManager, SpawnManager, EconomyManager, BuyZone,
  RoundManager, BuyMenuHandler, BombObjective class_name references
- Updated server config to match ServerConfig.gd format

Gray screen root cause: server scripts failed to parse in headless
mode due to Godot 4 class_name loading order (Resource after Node),
leaving server_main.gd non-functional — accepted connections but
never spawned players.

server/scripts/economy/buy_menu_handler.gd

@@ -23,6 +23,8 @@
 class_name BuyMenuHandler
 extends Node
 
+const _td = preload("res://scripts/teams/team_data.gd")
+
 # ---------------------------------------------------------------------------
 # Signals
 # ---------------------------------------------------------------------------
@@ -84,7 +86,7 @@ func is_player_in_buyzone(player_id: int) -> bool:
             # No buy zones means players can buy anywhere (dev fallback)
             return true
 
-    var player_team: TeamData.Team = TeamData.Team.SPECTATOR
+    var player_team: int = TeamData.Team.SPECTATOR
     if team_manager:
         player_team = team_manager.get_player_team(player_id)