chore: release version 2.3.5 and refactor lobby

Bump export_presets.cfg version to 2.3.5. Update CHANGELOG_DRAFT.md.
Refactor lobby.gd into LobbyChat, LobbyMainMenu, LobbyRoomList, LobbyRoom.
Move Nakama config to environment variables in nakama_manager.gd.
Derive auth_manager.gd encryption key from OS.get_unique_id().sha256_text().
Remove Steam email auth fallback. Require auth ticket.
Make GachaManager.pull() async in gacha_panel.gd.
Remove dummy wallet seeding. Add store_type to IAP payload.
Validate IAP receipts server-side in economy.lua.
Register gacha module in main.lua.
Clean backend_service.gd stubs.
Fix featured_banners type safety in gacha_manager.gd. Guards non-array responses.
Move tiles_armagedon_a1.res to assets/models/meshes/. Fix import fallback_path.

addons/gut/gui/ResizeHandle.tscn

@@ -0,0 +1,8 @@
+[gd_scene load_steps=2 format=3 uid="uid://bvrqqgjpyouse"]
+
+[ext_resource type="Script" uid="uid://duf6rfdqr6yoc" path="res://addons/gut/gui/ResizeHandle.gd" id="1_oi5ed"]
+
+[node name="ResizeHandle" type="ColorRect"]
+custom_minimum_size = Vector2(20, 20)
+color = Color(1, 1, 1, 0)
+script = ExtResource("1_oi5ed")