feat(engine): add Menu dropdown for Stats/Achievements/Profile/Settings/Leaderboard

Continues the UI-first pass. The five informational overlays were
each behind a single-key shortcut (S/A/P/O/L) with no visible UI
affordance. Add a "Menu ▾" button to the action bar that toggles a
popover with one row per overlay. Each row dispatches the same code
path the keyboard accelerator uses by writing a new
`Toggle*RequestEvent`:

- Stats        → ToggleStatsRequestEvent
- Achievements → ToggleAchievementsRequestEvent
- Profile      → ToggleProfileRequestEvent
- Settings     → ToggleSettingsRequestEvent
- Leaderboard  → ToggleLeaderboardRequestEvent

Each plugin's existing toggle handler now reads either its key or
the matching request event so the spawn / despawn / fetch logic stays
in the owning plugin (the popover never duplicates that behaviour).

Action bar order is now (left → right):
  Menu ▾   Undo   Pause   Help   Modes ▾   New Game

Menu sits on the far left because it's a navigation aggregator;
New Game stays on the far right as the most consequential action.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

solitaire_engine/src/settings_plugin.rs

@@ -16,7 +16,7 @@ use bevy::prelude::*;
 use solitaire_core::game_state::DrawMode;
 use solitaire_data::{load_settings_from, save_settings_to, settings_file_path, settings::Theme, AnimSpeed, Settings};
 
-use crate::events::ManualSyncRequestEvent;
+use crate::events::{ManualSyncRequestEvent, ToggleSettingsRequestEvent};
 use crate::progress_plugin::ProgressResource;
 use crate::resources::{SettingsScrollPos, SyncStatus, SyncStatusResource};
 
@@ -146,6 +146,7 @@ impl Plugin for SettingsPlugin {
             .init_resource::<SettingsScrollPos>()
             .add_message::<SettingsChangedEvent>()
             .add_message::<ManualSyncRequestEvent>()
+            .add_message::<ToggleSettingsRequestEvent>()
             .add_message::<bevy::input::mouse::MouseWheel>()
             .add_systems(Update, (handle_volume_keys, toggle_settings_screen, scroll_settings_panel));
 
@@ -206,12 +207,15 @@ fn handle_volume_keys(
     changed.write(SettingsChangedEvent(settings.0.clone()));
 }
 
-/// Opens or closes the Settings panel when `O` is pressed.
+/// Opens or closes the Settings panel — `O` keyboard accelerator or
+/// `ToggleSettingsRequestEvent` from the HUD Menu popover.
 fn toggle_settings_screen(
     keys: Res<ButtonInput<KeyCode>>,
+    mut requests: MessageReader<ToggleSettingsRequestEvent>,
     mut screen: ResMut<SettingsScreen>,
 ) {
-    if keys.just_pressed(KeyCode::KeyO) {
+    let button_clicked = requests.read().count() > 0;
+    if keys.just_pressed(KeyCode::KeyO) || button_clicked {
         screen.0 = !screen.0;
     }
 }