feat(nav): discoverable sidebar — instant tooltips, shortcuts made visible, pinnable rail

The icon-only rail forced first-time users to guess (usertest:
Senior, a11y, UX personas). Three changes:
- Nav tooltips appear instantly and carry the page shortcut
  (Cmd+1..9, Ctrl on non-mac — Ctrl activators added); expanded
  labels show the same hint. Explicit button semantics for
  screen readers on every destination.
- A visible 'Search & commands' row above the footer opens the
  existing Cmd+K palette, which nothing in the UI advertised.
- Settings -> Appearance gains 'Keep the navigation expanded':
  pins the rail with permanent labels (persisted preference).
Footer strip and pillar toggle made overflow-safe for the
animating rail; responsive test scrolls the by-design scrollable
destinations list.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_de.arb

@@ -1549,6 +1549,9 @@
   "doctorPathStudioErrors": "Studio-Fehler",
   "settingsCategoryGeneral": "Allgemein",
   "settingsCategoryAppearance": "Darstellung",
+  "sidebarSearchLabel": "Suchen & Befehle",
+  "settingsSidebarPinnedTitle": "Navigation immer ausgeklappt",
+  "settingsSidebarPinnedBody": "Zeigt die Beschriftungen der Seitenleiste dauerhaft an, statt sie nur beim Überfahren mit der Maus einzublenden.",
   "settingsCategoryAi": "System-KI",
   "settingsCategoryIntegrations": "Integrationen",
   "settingsCategorySecurity": "Sicherheit",

lib/l10n/app_en.arb

@@ -1573,6 +1573,9 @@
   "doctorPathStudioErrors": "Studio errors",
   "settingsCategoryGeneral": "General",
   "settingsCategoryAppearance": "Appearance",
+  "sidebarSearchLabel": "Search & commands",
+  "settingsSidebarPinnedTitle": "Keep the navigation expanded",
+  "settingsSidebarPinnedBody": "Shows the sidebar labels permanently instead of only while hovering with the mouse.",
   "settingsCategoryAi": "System AI",
   "settingsCategoryIntegrations": "Integrations",
   "settingsCategorySecurity": "Security",

lib/l10n/app_localizations.dart

@@ -4544,6 +4544,24 @@ abstract class AppLocalizations {
   /// **'Appearance'**
   String get settingsCategoryAppearance;
 
+  /// No description provided for @sidebarSearchLabel.
+  ///
+  /// In en, this message translates to:
+  /// **'Search & commands'**
+  String get sidebarSearchLabel;
+
+  /// No description provided for @settingsSidebarPinnedTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Keep the navigation expanded'**
+  String get settingsSidebarPinnedTitle;
+
+  /// No description provided for @settingsSidebarPinnedBody.
+  ///
+  /// In en, this message translates to:
+  /// **'Shows the sidebar labels permanently instead of only while hovering with the mouse.'**
+  String get settingsSidebarPinnedBody;
+
   /// No description provided for @settingsCategoryAi.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -2666,6 +2666,16 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get settingsCategoryAppearance => 'Darstellung';
 
+  @override
+  String get sidebarSearchLabel => 'Suchen & Befehle';
+
+  @override
+  String get settingsSidebarPinnedTitle => 'Navigation immer ausgeklappt';
+
+  @override
+  String get settingsSidebarPinnedBody =>
+      'Zeigt die Beschriftungen der Seitenleiste dauerhaft an, statt sie nur beim Überfahren mit der Maus einzublenden.';
+
   @override
   String get settingsCategoryAi => 'System-KI';
 

lib/l10n/app_localizations_en.dart

@@ -2668,6 +2668,16 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get settingsCategoryAppearance => 'Appearance';
 
+  @override
+  String get sidebarSearchLabel => 'Search & commands';
+
+  @override
+  String get settingsSidebarPinnedTitle => 'Keep the navigation expanded';
+
+  @override
+  String get settingsSidebarPinnedBody =>
+      'Shows the sidebar labels permanently instead of only while hovering with the mouse.';
+
   @override
   String get settingsCategoryAi => 'System AI';