P7.9: fix headless export — resolve Resource class_name ordering + duplicate RoundManager + simulation stub API

- Fix dead code in server_main.gd (unreachable lag compensation print)
- Remove WeaponData type hints from weapon_server.gd (Resource class_name in Node scripts = headless fail)
- Use preload() instead of WeaponData class_name in weapon_definitions.gd for const refs
- Lazy-init WEAPONS dict (const can't reference preload members)
- Remove duplicate class_name RoundManager from server/scripts/round/round_manager.gd
- Remove DamageProcessor type hints from round/round_manager.gd and bomb_objective.gd
- Add start()/stop()/can_tick()/tick()/spawn_entity()/despawn_entity() to simulation_server_stub.gd
- Fix get_world_3d() → get_tree().root.world_3d in weapon_server.gd Node context
- Fix var data := → var data = for untyped WeaponDefinitions.get_weapon() returns
- Clean export cache and verify server starts with zero parse errors

server/scripts/combat/lag_compensation.gd

@@ -7,9 +7,17 @@ extends Node
 var physics_world = null
 var _history: Dictionary = {}  # tick → { entity_id: position }
 
+## Record the start of a new tick for lag compensation.
+## Called by GameServer each tick before processing inputs.
+## Individual player positions are recorded by the game server loop.
+func record_tick(tick: int) -> void:
+	_history[tick] = {}
+
+## Record a player's position at a given tick (used during per-entity processing).
 func record_position(tick: int, entity_id: int, position: Vector3) -> void:
-	_history[tick] = {entity_id: position}
-	# Keep only 128 most recent ticks
+	if not _history.has(tick):
+		_history[tick] = {}
+	_history[tick][entity_id] = position
 	if _history.size() > 128:
 		var oldest = _history.keys().min()
 		if oldest != null: