fix(ui): loading screen blocks input + main menu polls during catalog wait

- loading_screen: opaque BG (was 0.75 alpha) + mouse_filter STOP so the
  loading state genuinely occludes the underlying screen
- main_menu: poll SimBridge.poll_snapshot in _process while waiting for
  the bookmark catalog so the new-game flow doesn't stall on the
  catalog round-trip introduced in Workstream 3 (#680)

client/ui/meta/screens/loading/loading_screen.gd

@@ -4,7 +4,7 @@ extends MetaScreen
 ## Full-screen, dark overlay with centered status text.
 ## #724: Shows client version (from project.yaml) and protocol version below the status text.
 
-const BG_COLOR := Color(0.0, 0.0, 0.0, 0.75)
+const BG_COLOR := Color(0.05, 0.05, 0.08, 1.0)
 const TEXT_COLOR := Color("#c8d0e0")
 const VERSION_COLOR := Color("#667788")
 const FONT_SIZE := 18
@@ -17,7 +17,7 @@ var _version_label: Label = null
 func _ready() -> void:
 	closable_by_escape = false
 	visible = false
-	mouse_filter = Control.MOUSE_FILTER_IGNORE
+	mouse_filter = Control.MOUSE_FILTER_STOP
 	set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)
 	_build_ui()
 

client/ui/meta/screens/main_menu/main_menu.gd

@@ -62,6 +62,11 @@ func _on_new_game() -> void:
 	SimBridge.connect_to_sim()
 
 
+func _process(_delta: float) -> void:
+	if _waiting_for_catalog:
+		SimBridge.poll_snapshot()
+
+
 func _ensure_loading_screen() -> void:
 	if _loading_screen != null and is_instance_valid(_loading_screen):
 		return