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/objectives/bomb_objective.gd

@@ -81,13 +81,13 @@ const DEFAULT_EXPLOSION_DAMAGE: float = 500.0
 # ---------------------------------------------------------------------------
 
 ## Reference to the RoundManager node.
-var round_manager: RoundManager = null
+var round_manager = null
 
 ## Reference to the TeamManager for checking player teams.
-var team_manager: TeamManager = null
+var team_manager = null
 
 ## Reference to the DamageProcessor for applying explosion damage.
-var damage_processor: DamageProcessor = null
+var damage_processor = null  # DamageProcessor — untyped for headless compat
 
 ## Mapping: entity_id → peer_id (from GameServer).
 var entity_to_peer: Dictionary = {}