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/DeadlineTrafficLights.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { useEffect, useRef } from "react";
+import Link from "next/link";
 import { AlertTriangle, Clock, CheckCircle } from "lucide-react";
 import type { DeadlineSummary } from "@/lib/types";
 
@@ -27,10 +28,9 @@ function AnimatedCount({ value }: { value: number }) {
 
 interface Props {
   data: DeadlineSummary;
-  onFilter?: (filter: "overdue" | "this_week" | "ok") => void;
 }
 
-export function DeadlineTrafficLights({ data, onFilter }: Props) {
+export function DeadlineTrafficLights({ data }: Props) {
   const safe = data ?? { overdue_count: 0, due_this_week: 0, due_next_week: 0, ok_count: 0 };
   const cards = [
     {
@@ -38,6 +38,7 @@ export function DeadlineTrafficLights({ data, onFilter }: Props) {
       label: "Überfällig",
       count: safe.overdue_count ?? 0,
       icon: AlertTriangle,
+      href: "/fristen?status=overdue",
       bg: "bg-red-50",
       border: "border-red-200",
       iconColor: "text-red-500",
@@ -51,6 +52,7 @@ export function DeadlineTrafficLights({ data, onFilter }: Props) {
       label: "Diese Woche",
       count: safe.due_this_week ?? 0,
       icon: Clock,
+      href: "/fristen?status=this_week",
       bg: "bg-amber-50",
       border: "border-amber-200",
       iconColor: "text-amber-500",
@@ -64,6 +66,7 @@ export function DeadlineTrafficLights({ data, onFilter }: Props) {
       label: "Im Zeitplan",
       count: (safe.ok_count ?? 0) + (safe.due_next_week ?? 0),
       icon: CheckCircle,
+      href: "/fristen?status=ok",
       bg: "bg-emerald-50",
       border: "border-emerald-200",
       iconColor: "text-emerald-500",
@@ -77,9 +80,9 @@ export function DeadlineTrafficLights({ data, onFilter }: Props) {
   return (
     <div className="grid grid-cols-1 gap-4 sm:grid-cols-3">
       {cards.map((card) => (
-        <button
+        <Link
           key={card.key}
-          onClick={() => onFilter?.(card.key)}
+          href={card.href}
           className={`group relative overflow-hidden rounded-xl border ${card.border} ${card.bg} ${card.ring} p-6 text-left transition-all hover:shadow-md active:scale-[0.98]`}
         >
           {card.pulse && (
@@ -99,7 +102,7 @@ export function DeadlineTrafficLights({ data, onFilter }: Props) {
           <div className={`mt-4 text-4xl font-bold tracking-tight ${card.countColor}`}>
             <AnimatedCount value={card.count} />
           </div>
-        </button>
+        </Link>
       ))}
     </div>
   );