feat: reporting dashboard — case stats, deadline compliance, workload, billing (P1)

Backend:
- ReportingService with aggregation queries (CTEs, FILTER clauses)
- 4 API endpoints: /api/reports/{cases,deadlines,workload,billing}
- Date range filtering via ?from=&to= query params

Frontend:
- /berichte page with 4 tabs: Akten, Fristen, Auslastung, Abrechnung
- recharts: bar/pie/line charts for all report types
- Date range picker, CSV export, print-friendly view
- Sidebar nav entry with BarChart3 icon

Also resolves merge conflicts between role-based, notification, and
audit trail branches, and adds missing TS types (AuditLogResponse,
Notification, NotificationPreferences).

frontend/src/components/reports/CasesTab.tsx

@@ -0,0 +1,223 @@
+"use client";
+
+import type { CaseReport } from "@/lib/types";
+import {
+  BarChart,
+  Bar,
+  XAxis,
+  YAxis,
+  CartesianGrid,
+  Tooltip,
+  ResponsiveContainer,
+  Legend,
+  PieChart,
+  Pie,
+  Cell,
+} from "recharts";
+import { FolderOpen, TrendingUp, TrendingDown } from "lucide-react";
+
+const COLORS = [
+  "#171717",
+  "#525252",
+  "#a3a3a3",
+  "#d4d4d4",
+  "#737373",
+  "#404040",
+  "#e5e5e5",
+  "#262626",
+];
+
+function formatMonth(period: string): string {
+  const [year, month] = period.split("-");
+  const months = [
+    "Jan",
+    "Feb",
+    "Mär",
+    "Apr",
+    "Mai",
+    "Jun",
+    "Jul",
+    "Aug",
+    "Sep",
+    "Okt",
+    "Nov",
+    "Dez",
+  ];
+  return `${months[parseInt(month, 10) - 1]} ${year.slice(2)}`;
+}
+
+export function CasesTab({ data }: { data: CaseReport }) {
+  const chartData = data.monthly.map((m) => ({
+    ...m,
+    name: formatMonth(m.period),
+  }));
+
+  return (
+    <div className="space-y-6">
+      {/* Summary cards */}
+      <div className="grid grid-cols-1 gap-4 sm:grid-cols-3">
+        <div className="rounded-xl border border-neutral-200 bg-white p-5">
+          <div className="flex items-center gap-2 text-sm text-neutral-500">
+            <FolderOpen className="h-4 w-4" />
+            Eröffnet
+          </div>
+          <p className="mt-2 text-2xl font-semibold text-neutral-900">
+            {data.total.opened}
+          </p>
+        </div>
+        <div className="rounded-xl border border-neutral-200 bg-white p-5">
+          <div className="flex items-center gap-2 text-sm text-neutral-500">
+            <TrendingDown className="h-4 w-4" />
+            Geschlossen
+          </div>
+          <p className="mt-2 text-2xl font-semibold text-neutral-900">
+            {data.total.closed}
+          </p>
+        </div>
+        <div className="rounded-xl border border-neutral-200 bg-white p-5">
+          <div className="flex items-center gap-2 text-sm text-neutral-500">
+            <TrendingUp className="h-4 w-4" />
+            Aktiv
+          </div>
+          <p className="mt-2 text-2xl font-semibold text-emerald-600">
+            {data.total.active}
+          </p>
+        </div>
+      </div>
+
+      {/* Bar chart: opened/closed per month */}
+      <div className="rounded-xl border border-neutral-200 bg-white p-5">
+        <h3 className="mb-4 text-sm font-medium text-neutral-900">
+          Akten pro Monat
+        </h3>
+        {chartData.length === 0 ? (
+          <p className="py-8 text-center text-sm text-neutral-400">
+            Keine Daten im gewählten Zeitraum
+          </p>
+        ) : (
+          <ResponsiveContainer width="100%" height={300}>
+            <BarChart data={chartData}>
+              <CartesianGrid strokeDasharray="3 3" stroke="#e5e5e5" />
+              <XAxis dataKey="name" tick={{ fontSize: 12 }} stroke="#a3a3a3" />
+              <YAxis
+                allowDecimals={false}
+                tick={{ fontSize: 12 }}
+                stroke="#a3a3a3"
+              />
+              <Tooltip
+                contentStyle={{
+                  border: "1px solid #e5e5e5",
+                  borderRadius: 8,
+                  fontSize: 13,
+                }}
+              />
+              <Legend wrapperStyle={{ fontSize: 13 }} />
+              <Bar
+                dataKey="opened"
+                name="Eröffnet"
+                fill="#171717"
+                radius={[4, 4, 0, 0]}
+              />
+              <Bar
+                dataKey="closed"
+                name="Geschlossen"
+                fill="#a3a3a3"
+                radius={[4, 4, 0, 0]}
+              />
+            </BarChart>
+          </ResponsiveContainer>
+        )}
+      </div>
+
+      {/* Pie charts row */}
+      <div className="grid grid-cols-1 gap-6 lg:grid-cols-2">
+        {/* By type */}
+        <div className="rounded-xl border border-neutral-200 bg-white p-5">
+          <h3 className="mb-4 text-sm font-medium text-neutral-900">
+            Nach Verfahrensart
+          </h3>
+          {data.by_type.length === 0 ? (
+            <p className="py-8 text-center text-sm text-neutral-400">
+              Keine Daten
+            </p>
+          ) : (
+            <div className="flex items-center gap-4">
+              <ResponsiveContainer width="50%" height={200}>
+                <PieChart>
+                  <Pie
+                    data={data.by_type}
+                    dataKey="count"
+                    nameKey="case_type"
+                    cx="50%"
+                    cy="50%"
+                    innerRadius={40}
+                    outerRadius={80}
+                  >
+                    {data.by_type.map((_, i) => (
+                      <Cell
+                        key={i}
+                        fill={COLORS[i % COLORS.length]}
+                      />
+                    ))}
+                  </Pie>
+                  <Tooltip />
+                </PieChart>
+              </ResponsiveContainer>
+              <div className="flex-1 space-y-2">
+                {data.by_type.map((item, i) => (
+                  <div key={i} className="flex items-center gap-2 text-sm">
+                    <div
+                      className="h-3 w-3 rounded-full"
+                      style={{
+                        backgroundColor: COLORS[i % COLORS.length],
+                      }}
+                    />
+                    <span className="text-neutral-600">{item.case_type}</span>
+                    <span className="ml-auto font-medium text-neutral-900">
+                      {item.count}
+                    </span>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
+        </div>
+
+        {/* By court */}
+        <div className="rounded-xl border border-neutral-200 bg-white p-5">
+          <h3 className="mb-4 text-sm font-medium text-neutral-900">
+            Nach Gericht
+          </h3>
+          {data.by_court.length === 0 ? (
+            <p className="py-8 text-center text-sm text-neutral-400">
+              Keine Daten
+            </p>
+          ) : (
+            <div className="space-y-3">
+              {data.by_court.map((item, i) => {
+                const maxCount = Math.max(...data.by_court.map((c) => c.count));
+                const pct = maxCount > 0 ? (item.count / maxCount) * 100 : 0;
+                return (
+                  <div key={i}>
+                    <div className="flex items-center justify-between text-sm">
+                      <span className="text-neutral-600">{item.court}</span>
+                      <span className="font-medium text-neutral-900">
+                        {item.count}
+                      </span>
+                    </div>
+                    <div className="mt-1 h-2 rounded-full bg-neutral-100">
+                      <div
+                        className="h-2 rounded-full bg-neutral-900 transition-all"
+                        style={{ width: `${pct}%` }}
+                      />
+                    </div>
+                  </div>
+                );
+              })}
+            </div>
+          )}
+        </div>
+      </div>
+    </div>
+  );
+}