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

export_presets.cfg

@@ -48,7 +48,7 @@ dedicated_server=true
 custom_features=""
 export_filter="all_resources"
 include_filter=""
-exclude_filter="client/**, server/server-browser-api/venv/**, **/venv/**"
+exclude_filter="client/**, gdextension.disabled/**, server/server-browser-api/venv/**, **/venv/**"
 export_path="build/tactical-shooter-server.x86_64"
 patches=PackedStringArray()
 encryption_include_filters=""