feat: enhance keyboard shortcuts and background image handling

- Added `GlobalKeyboardShortcuts` component to manage global keyboard shortcuts.
- Introduced new keyboard shortcut (Shift + B) for changing the background.
- Updated `BackgroundImageSelector` to preserve custom background URLs and allow restoration of previously set backgrounds.
- Improved local storage handling for custom backgrounds to enhance user experience.

src/app/layout.tsx

@@ -8,6 +8,7 @@ import { UserPreferencesProvider } from "@/contexts/UserPreferencesContext";
 import { KeyboardShortcutsProvider } from "@/contexts/KeyboardShortcutsContext";
 import { userPreferencesService } from "@/services/core/user-preferences";
 import { KeyboardShortcuts } from "@/components/KeyboardShortcuts";
+import { GlobalKeyboardShortcuts } from "@/components/GlobalKeyboardShortcuts";
 import { AuthProvider } from "../components/AuthProvider";
 import { getServerSession } from 'next-auth';
 import { authOptions } from '@/lib/auth';
@@ -55,6 +56,7 @@ export default async function RootLayout({
               <KeyboardShortcuts />
               <JiraConfigProvider config={initialPreferences?.jiraConfig || { enabled: false }}>
                 <UserPreferencesProvider initialPreferences={initialPreferences}>
+                  <GlobalKeyboardShortcuts />
                   <BackgroundProvider>
                     {children}
                   </BackgroundProvider>