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/double_templates/double_data_template.txt

@@ -0,0 +1,22 @@
+var __gutdbl_values = {
+	thepath = '{path}',
+	subpath = '{subpath}',
+	stubber = {stubber_id},
+	spy = {spy_id},
+	gut = {gut_id},
+	singleton_name = '{singleton_name}',
+	singleton = {singleton_id},
+	is_partial = {is_partial},
+	doubled_methods = {doubled_methods},
+}
+var __gutdbl = load('res://addons/gut/double_tools.gd').new(self)
+
+# Here so other things can check for a method to know if this is a double.
+func __gutdbl_check_method__():
+	pass
+
+# Cleanup called by GUT after tests have finished.  Important for RefCounted
+# objects.  Nodes are freed, and won't have this method called on them.
+func __gutdbl_done():
+	__gutdbl = null
+	__gutdbl_values.clear()