feat: Phase B — interactive dashboard, breadcrumbs, clickable navigation

- Breadcrumb component: reusable nav with items array (label+href)
- DeadlineTrafficLights: buttons → Links to /fristen?status={filter}
- CaseOverviewGrid: static metrics → clickable Links to /cases?status={filter}
- UpcomingTimeline: items → clickable Links to /fristen/{id} or /termine/{id}
  with case number links and hover chevron
- QuickActions: swap CalDAV Sync for "Neuer Termin" → /termine/neu,
  fix "Frist eintragen" → /fristen/neu
- AISummaryCard: add RefreshCw button with spinning animation
- RecentActivityList: new component showing recent case events
- DeadlineList: accept initialStatus prop, add this_week/ok filters
- fristen/page.tsx: read searchParams.status for initial filter
- Add breadcrumbs to dashboard, fristen, cases, termine pages
- Add RecentActivity type, update DashboardData type

frontend/src/components/dashboard/RecentActivityList.tsx

@@ -0,0 +1,80 @@
+"use client";
+
+import Link from "next/link";
+import { formatDistanceToNow, parseISO } from "date-fns";
+import { de } from "date-fns/locale";
+import {
+  FileText,
+  Scale,
+  Calendar,
+  Clock,
+  MessageSquare,
+  ChevronRight,
+} from "lucide-react";
+import type { RecentActivity } from "@/lib/types";
+
+const EVENT_ICONS: Record<string, typeof FileText> = {
+  status_changed: Scale,
+  deadline_created: Clock,
+  appointment_created: Calendar,
+  document_uploaded: FileText,
+  note_added: MessageSquare,
+};
+
+interface Props {
+  activities: RecentActivity[];
+}
+
+export function RecentActivityList({ activities }: Props) {
+  const safe = Array.isArray(activities) ? activities : [];
+
+  if (safe.length === 0) {
+    return null;
+  }
+
+  return (
+    <div className="rounded-xl border border-neutral-200 bg-white p-5">
+      <h2 className="text-sm font-semibold text-neutral-900">
+        Letzte Aktivität
+      </h2>
+      <div className="mt-3 divide-y divide-neutral-100">
+        {safe.map((activity) => {
+          const Icon = EVENT_ICONS[activity.event_type ?? ""] ?? FileText;
+          const timeAgo = activity.created_at
+            ? formatDistanceToNow(parseISO(activity.created_at), {
+                addSuffix: true,
+                locale: de,
+              })
+            : "";
+
+          return (
+            <Link
+              key={activity.id}
+              href={`/cases/${activity.case_id}`}
+              className="group flex items-center gap-3 py-2.5 transition-colors first:pt-0 last:pb-0 hover:bg-neutral-50 -mx-5 px-5"
+            >
+              <div className="rounded-md bg-neutral-100 p-1.5">
+                <Icon className="h-3.5 w-3.5 text-neutral-500" />
+              </div>
+              <div className="min-w-0 flex-1">
+                <p className="truncate text-sm text-neutral-900">
+                  {activity.title}
+                </p>
+                <div className="flex items-center gap-2 text-xs text-neutral-500">
+                  <span>{activity.case_number}</span>
+                  {timeAgo && (
+                    <>
+                      <span className="text-neutral-300">·</span>
+                      <span>{timeAgo}</span>
+                    </>
+                  )}
+                </div>
+              </div>
+              <ChevronRight className="h-4 w-4 shrink-0 text-neutral-300 transition-colors group-hover:text-neutral-500" />
+            </Link>
+          );
+        })}
+      </div>
+    </div>
+  );
+}