feat(engine): tabbed Settings panel — Phase A of the menu redesign

Replaces the 37-row single-scroll settings modal with five tabs
(Audio, Gameplay, Appearance, Accessibility, Account); only the active
tab's rows spawn, so every tab fits without scroll-hunting.

- SettingsTab + ActiveSettingsTab (session-only) + SettingsTabButton
  chips under the modal header; rebuild-on-switch mirrors the
  leaderboard despawn/respawn pattern via a shared build_panel helper
- Accessibility tab gathers color-blind, high-contrast, reduce-motion,
  touch-input, and tooltip-delay from the old Gameplay/Cosmetic mix;
  Account = Sync + Privacy
- SettingsButton enum, input handlers, and persistence untouched
- Tests: per-tab Focusable/Tooltip sweeps, tab-switch rebuild test,
  picker/thumbnail tests pinned to the Appearance tab

Plan: docs/ui-redesign-2026-07.md (also added, phases A–M)

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

solitaire_engine/src/settings_plugin/mod.rs

@@ -170,6 +170,51 @@ struct SmartDefaultSizeText;
 #[derive(Component, Debug)]
 struct AnalyticsEnabledText;
 
+/// Which tab of the Settings panel is showing. Tabs replace the old
+/// single-scroll five-section layout (Phase A of
+/// `docs/ui-redesign-2026-07.md`) so each group fits on screen without
+/// scroll-hunting.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub(super) enum SettingsTab {
+    #[default]
+    Audio,
+    Gameplay,
+    Appearance,
+    Accessibility,
+    Account,
+}
+
+impl SettingsTab {
+    /// Every tab, in display order.
+    pub(super) const ALL: [Self; 5] = [
+        Self::Audio,
+        Self::Gameplay,
+        Self::Appearance,
+        Self::Accessibility,
+        Self::Account,
+    ];
+
+    /// Chip label.
+    pub(super) fn label(self) -> &'static str {
+        match self {
+            Self::Audio => "Audio",
+            Self::Gameplay => "Gameplay",
+            Self::Appearance => "Appearance",
+            Self::Accessibility => "Access",
+            Self::Account => "Account",
+        }
+    }
+}
+
+/// The active Settings tab. Session-only — deliberately not persisted;
+/// reopening Settings within a session returns to the last tab.
+#[derive(Resource, Debug, Default)]
+pub(super) struct ActiveSettingsTab(pub(super) SettingsTab);
+
+/// Marker on each tab chip button in the Settings header row.
+#[derive(Component, Debug)]
+pub(super) struct SettingsTabButton(pub(super) SettingsTab);
+
 /// Marks the scrollable inner card so the mouse-wheel system can target it.
 #[derive(Component, Debug)]
 struct SettingsPanelScrollable;
@@ -369,6 +414,7 @@ impl Plugin for SettingsPlugin {
             .insert_resource(SettingsStoragePath(self.storage_path.clone()))
             .init_resource::<SettingsScreen>()
             .init_resource::<SettingsScrollPos>()
+            .init_resource::<ActiveSettingsTab>()
             .init_resource::<PendingWindowGeometry>()
             .add_message::<SettingsChangedEvent>()
             .add_message::<ManualSyncRequestEvent>()
@@ -423,7 +469,15 @@ impl Plugin for SettingsPlugin {
             app.add_systems(
                 Update,
                 (
-                    sync_settings_panel_visibility,
+                    // Chained: a tab click must observe this frame's
+                    // visibility state, and the rebuild must observe the
+                    // click — total order avoids panel double-spawns.
+                    (
+                        sync_settings_panel_visibility,
+                        handle_tab_buttons,
+                        rebuild_panel_on_tab_change,
+                    )
+                        .chain(),
                     handle_settings_buttons,
                     handle_sync_buttons,
                     #[cfg(not(target_arch = "wasm32"))]