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.

scripts/services/backend_service.gd

@@ -61,59 +61,7 @@ func _connect_nakama_signals() -> void:
 	# No need to connect through BackendService
 	pass
 
-## Achievement Methods
-# All platforms use Nakama for achievements
 
-func unlock_achievement(achievement_id: String) -> void:
-	if nakama_backend:
-		# Nakama achievement implementation
-		pass
-
-func set_achievement_progress(achievement_id: String, current: int, max: int) -> void:
-	if nakama_backend:
-		# Nakama progress implementation
-		pass
-
-func get_achievement_progress(achievement_id: String) -> Dictionary:
-	if nakama_backend:
-		# Nakama get progress implementation
-		pass
-	return {}
-
-func get_all_achievements() -> Array:
-	if nakama_backend:
-		# Nakama get all achievements implementation
-		pass
-	return []
-
-## Leaderboard Methods
-# All platforms use Nakama for leaderboards
-
-func submit_leaderboard_score(leaderboard_id: String, score: int) -> void:
-	if nakama_backend:
-		# Nakama leaderboard submission - use UserProfileManager.submit_to_leaderboard()
-		await UserProfileManager.submit_to_leaderboard()
-
-func get_leaderboard_entries(leaderboard_id: String, range_start: int = 1, range_end: int = 10) -> void:
-	if nakama_backend:
-		# Nakama get leaderboard entries - use LeaderboardPanel._fetch_leaderboard_data()
-		# This is handled by the UI panel directly
-		pass
-
-## Shop Methods
-# All platforms use Nakama for shop
-
-func purchase_shop_item(item_id: String) -> void:
-	if nakama_backend:
-		# Nakama shop purchase - use UserProfileManager.purchase_item()
-		# This is handled by the UI panel directly via ShopPanel
-		pass
-
-func get_shop_items() -> void:
-	if nakama_backend:
-		# Nakama get shop items - use UserProfileManager.fetch_shop_catalog()
-		# This is handled by the UI panel directly via ShopPanel
-		pass
 
 ## Utility Methods