feat(engine): group HUD menu popover into Play/You/Community/System sections

Phase C of docs/ui-redesign-2026-07.md. The Modes row is gone — Home
owns mode selection, so the popover's Play section carries a Home row
firing the new ToggleHomeRequestEvent (read by toggle_home_screen
alongside the existing M accelerator). Section headers are quiet
caption-size labels inside the existing panel widget, not a new
widget. The action-bar Modes button and its popover are untouched
(their removal is Phase B territory when Home gains hierarchy).

- MenuOption: Modes variant replaced by Home; rows grouped Play (Home)
  · You (Profile, Stats, Achievements) · Community (Leaderboard) ·
  System (Settings, Help)
- handle_menu_option_click no longer chains into spawn_modes_popover
- Tests: tooltip sweep updated (7 rows still), new
  toggle_home_event_opens_home_screen covers the popover's open path

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/events.rs

@@ -237,6 +237,11 @@ pub struct ToggleSettingsRequestEvent;
 #[derive(Message, Debug, Clone, Copy, Default)]
 pub struct ToggleLeaderboardRequestEvent;
 
+/// Request to toggle the Home mode launcher. Fired by the HUD
+/// Menu-popover "Home" row alongside the existing `M` accelerator.
+#[derive(Message, Debug, Clone, Copy, Default)]
+pub struct ToggleHomeRequestEvent;
+
 /// Fired by `SyncPlugin` after a pull task resolves and the merged result has
 /// been persisted to disk. `Ok(SyncResponse)` carries the merged payload plus
 /// any `ConflictReport`s the merge produced. `Err(String)` carries a