feat: add frontend case list, detail, and creation pages (Phase 1F)

- Case list page (/cases) with search, status/type filters, status badges
- Case creation page (/cases/new) with reusable CaseForm component
- Case detail page (/cases/[id]) with tabs: Timeline, Deadlines, Documents, Parties
- CaseTimeline component for chronological case_events display
- PartyList component with inline party CRUD (add/delete)
- Updated sidebar navigation to route to /cases

frontend/src/components/cases/CaseTimeline.tsx

@@ -0,0 +1,60 @@
+"use client";
+
+import type { CaseEvent } from "@/lib/types";
+import { format } from "date-fns";
+import { de } from "date-fns/locale";
+
+const EVENT_ICONS: Record<string, string> = {
+  case_created: "bg-emerald-500",
+  status_changed: "bg-amber-500",
+  party_added: "bg-blue-500",
+  case_archived: "bg-neutral-400",
+  document_uploaded: "bg-violet-500",
+  deadline_created: "bg-red-500",
+};
+
+interface CaseTimelineProps {
+  events: CaseEvent[];
+}
+
+export function CaseTimeline({ events }: CaseTimelineProps) {
+  if (events.length === 0) {
+    return (
+      <p className="py-8 text-center text-sm text-neutral-400">
+        Keine Ereignisse vorhanden.
+      </p>
+    );
+  }
+
+  return (
+    <div className="relative space-y-0">
+      {events.map((event, i) => (
+        <div key={event.id} className="relative flex gap-3 pb-6">
+          {i < events.length - 1 && (
+            <div className="absolute left-[7px] top-4 h-full w-px bg-neutral-200" />
+          )}
+          <div
+            className={`mt-1 h-[15px] w-[15px] shrink-0 rounded-full border-2 border-white ${EVENT_ICONS[event.event_type ?? ""] ?? "bg-neutral-300"}`}
+          />
+          <div className="min-w-0 flex-1">
+            <p className="text-sm font-medium text-neutral-900">
+              {event.title}
+            </p>
+            {event.description && (
+              <p className="mt-0.5 text-sm text-neutral-500">
+                {event.description}
+              </p>
+            )}
+            <p className="mt-1 text-xs text-neutral-400">
+              {format(
+                new Date(event.event_date ?? event.created_at),
+                "d. MMM yyyy, HH:mm",
+                { locale: de },
+              )}
+            </p>
+          </div>
+        </div>
+      ))}
+    </div>
+  );
+}