feat(client): Option A pre-game flow + ESC priority chain (Workstream 4)

main_menu now connects SimBridge before character_creation opens, gating
the transition on first ObserverSnapshot carrying a bookmark_catalog.
Loading screen is shown during the connect; on cancel the SimBridge
subprocess is torn down and the player returns to main_menu. Catalog is
read straight from GameState.bookmark_catalog in W6.

Flow (Option A):
1. New Game → SessionManager.new_game() creates save dir
2. main_menu pushes loading_screen via MetaStack with "Connecting to
   simulation..." message
3. SimBridge.connect_to_sim() spawned; main_menu listens on
   connection_state_changed, then on snapshot_received for the catalog
4. On catalog arrival: loading_screen closed, scene-transition to
   character_creation
5. character_creation Cancel → SimBridge.disconnect_from_sim() + scene
   transition back to main_menu (Tyre's recommendation: clean state per
   session over warm-start savings)
6. character_creation Start → ConfirmBookmark sent (stubbed for W4 with
   first catalog entry; real bookmark + location from W6's UI)

ESC priority chain in main.gd OPEN_MENU handler:
- MetaStack.handle_escape() first — closes the topmost meta overlay
- HudGroups.is_implant_active() / close_app() — closes active implant
- Fallback: toggle settings_dialog (existing W2 behavior)

Files:
- sim_bridge.gd: send_named_action(action_name, action_data) helper.
  Bridges named tag-enum PlayerActions (RequestBookmarkCatalog,
  ConfirmBookmark) into the existing outbound buffer, parallel to
  send_input's InputMapper.Action handling.
- loading_screen.gd: set_message(text) for the connecting/loading label.
- main_menu.gd: full Option A flow rewrite. Tracks _waiting_for_catalog
  so re-clicking New Game during connect is a no-op.
- character_creation.gd: _on_back disconnect path + _on_start
  ConfirmBookmark stub. MAIN_MENU_SCENE / GAME_SCENE constants.
- main.gd: connect_to_sim guard (don't reconnect when Option A leaves
  it CONNECTED). ESC chain wiring.

Verification:
- gdlint clean
- godot --headless --path client --quit — no SCRIPT ERROR
- test_protocol 62/62, test_implant_nav_stack 52/52, test_client_p3
  24/24, test_ui_framework_sprint15 54/54

Pre-existing failing suites unchanged: test_sprint2_proof,
test_dialogue_sprint18, test_client_p2 (camera-smoothing assertions
that pre-date W4 — main.gd has disabled position_smoothing_enabled
since #117 / #501 / #117 manual-lerp; tests were stale).

Workstream 5 (3-tab restructure of character_creation: Bookmark /
Appearance with sub-nav / Skills / Debug) lands next.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -76,6 +76,12 @@ func _read_client_version() -> String:
 	return "?.?.?"
 
 
+## Update the status text shown while loading. Call before show_loading() or after.
+func set_message(text: String) -> void:
+	if _label != null:
+		_label.text = text
+
+
 func show_loading() -> void:
 	MetaStack.push(self)
 	open()