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/UserFileViewer.gd

@@ -0,0 +1,52 @@
+extends Window
+
+@onready var rtl = $TextDisplay/RichTextLabel
+
+func _get_file_as_text(path):
+	var to_return = null
+	var f = FileAccess.open(path, FileAccess.READ)
+	if(f != null):
+		to_return = f.get_as_text()
+	else:
+		to_return = str('ERROR:  Could not open file.  Error code ', FileAccess.get_open_error())
+	return to_return
+
+func _ready():
+	rtl.clear()
+
+func _on_OpenFile_pressed():
+	$FileDialog.popup_centered()
+
+func _on_FileDialog_file_selected(path):
+	show_file(path)
+
+func _on_Close_pressed():
+	self.hide()
+
+func show_file(path):
+	var text = _get_file_as_text(path)
+	if(text == ''):
+		text = '<Empty File>'
+	rtl.set_text(text)
+	self.window_title = path
+
+func show_open():
+	self.popup_centered()
+	$FileDialog.popup_centered()
+
+func get_rich_text_label():
+	return $TextDisplay/RichTextLabel
+
+func _on_Home_pressed():
+	rtl.scroll_to_line(0)
+
+func _on_End_pressed():
+	rtl.scroll_to_line(rtl.get_line_count() -1)
+
+func _on_Copy_pressed():
+	return
+	# OS.clipboard = rtl.text
+
+func _on_file_dialog_visibility_changed():
+	if rtl.text.length() == 0 and not $FileDialog.visible:
+		self.hide()