feat(i18n): migrate hardcoded German strings to t() across 104 components/pages — AST-based batch with re-parse gate, 423 new de.json keys; tsc clean; vitest failures byte-identical to clean-tree baseline (pre-existing)

frontend/src/components/layout/Sidebar.tsx

@@ -182,21 +182,21 @@ export function Sidebar() {
           'flex flex-col transition-transform motion-safe:duration-300',
           sidebarOpen ? 'translate-x-0' : '-translate-x-full md:hidden'
         )}
-        aria-label="Seitenleiste Navigation"
+        aria-label={t('sidebar.seitenleistenavigation')}
         data-testid="sidebar"
       >
         <div className="h-[58px] flex items-center gap-2 px-4 border-b border-secondary-700">
           <button
             onClick={() => navigate('/start')}
             className="p-1.5 rounded-md text-secondary-400 hover:bg-secondary-700 hover:text-white flex items-center justify-center focus:outline-none"
-            aria-label="Zurück zur Startseite"
-            title="Zurück zur Startseite"
+            aria-label={t('sidebar.zurückzurstartseite')}
+            title={t('sidebar.zurückzurstartseite')}
           >
             <ArrowLeft className="w-4 h-4" />
           </button>
           <span className="text-xl font-bold text-white">leocrm</span>
         </div>
-        <nav className="flex-1 overflow-y-auto py-4" aria-label="Hauptnavigation">
+        <nav className="flex-1 overflow-y-auto py-4" aria-label={t('sidebar.hauptnavigation')}>
           <ul className="space-y-1 px-2">
             {(() => {
               const groups = new Map<string, typeof allMenuItems>();