feat: integrate ToastProvider and enhance theme management

- Added `ToastProvider` to `RootLayout` for improved user feedback on theme changes.
- Updated `ThemeProvider` to display toast notifications with theme names and icons upon theme changes.
- Refactored theme-related imports to streamline code and improve maintainability.
- Simplified background cycling logic in `useBackgroundCycle` to utilize centralized background definitions.
- Cleaned up unused background definitions in `BackgroundContext` for better clarity and performance.

src/components/ui/Header.tsx

@@ -5,8 +5,7 @@ import { useJiraConfig } from '@/contexts/JiraConfigContext';
 import { usePathname } from 'next/navigation';
 import Link from 'next/link';
 import { useState } from 'react';
-import { Theme } from '@/lib/theme-config';
-import { THEME_CONFIG, getThemeMetadata } from '@/lib/theme-config';
+import { Theme, THEME_CONFIG, getThemeIcon } from '@/lib/ui-config';
 import { useKeyboardShortcutsModal } from '@/contexts/KeyboardShortcutsContext';
 import { AuthButton } from '@/components/AuthButton';
 import { useSession, signOut } from 'next-auth/react';
@@ -28,12 +27,10 @@ export function Header({ title = "TowerControl", subtitle = "Task Management", s
 
   // Liste des thèmes disponibles avec leurs labels et icônes
   const themes: { value: Theme; label: string; icon: string }[] = THEME_CONFIG.allThemes.map(themeValue => {
-    const metadata = getThemeMetadata(themeValue);
-    
     return {
       value: themeValue,
-      label: metadata.name,
-      icon: metadata.icon
+      label: themeValue.charAt(0).toUpperCase() + themeValue.slice(1).replace('_', ' '),
+      icon: getThemeIcon(themeValue)
     };
   });