feat: add frontend dashboard with traffic lights, timeline, and AI summary (Phase 2L)

Dashboard page at /dashboard with 5 components:
- DeadlineTrafficLights: RED/AMBER/GREEN cards with animated counts and pulse for overdue
- CaseOverviewGrid: active/new/closed case counts
- UpcomingTimeline: merged deadlines + appointments for next 7 days, grouped by day
- AISummaryCard: natural language summary generated from dashboard data
- QuickActions: shortcuts to create cases, deadlines, AI analysis, CalDAV sync

3-column responsive grid layout. Root / redirects to /dashboard.
Fetches from GET /api/dashboard with 60s auto-refresh via react-query.

frontend/src/components/dashboard/QuickActions.tsx

@@ -0,0 +1,53 @@
+"use client";
+
+import Link from "next/link";
+import { FolderPlus, Clock, Sparkles, CalendarSync } from "lucide-react";
+
+const actions = [
+  {
+    label: "Neue Akte",
+    href: "/akten?new=1",
+    icon: FolderPlus,
+    color: "text-blue-600 bg-blue-50 hover:bg-blue-100",
+  },
+  {
+    label: "Frist eintragen",
+    href: "/fristen?new=1",
+    icon: Clock,
+    color: "text-amber-600 bg-amber-50 hover:bg-amber-100",
+  },
+  {
+    label: "AI Analyse",
+    href: "/ai",
+    icon: Sparkles,
+    color: "text-violet-600 bg-violet-50 hover:bg-violet-100",
+  },
+  {
+    label: "CalDAV Sync",
+    href: "/einstellungen",
+    icon: CalendarSync,
+    color: "text-emerald-600 bg-emerald-50 hover:bg-emerald-100",
+  },
+];
+
+export function QuickActions() {
+  return (
+    <div className="rounded-xl border border-neutral-200 bg-white p-5">
+      <h2 className="text-sm font-semibold text-neutral-900">
+        Schnellzugriff
+      </h2>
+      <div className="mt-3 grid grid-cols-2 gap-2">
+        {actions.map((action) => (
+          <Link
+            key={action.label}
+            href={action.href}
+            className={`flex items-center gap-2 rounded-lg px-3 py-2.5 text-sm font-medium transition-colors ${action.color}`}
+          >
+            <action.icon className="h-4 w-4" />
+            {action.label}
+          </Link>
+        ))}
+      </div>
+    </div>
+  );
+}