client: standalone /stats page with charts, off the admin dashboard

Closes #40.

New /stats route (client/stats.html + src/stats/), served by the same
catch-all pattern as /admin. Reuses the admin login (STATS_PUBLIC env var
on the server side decides whether it needs one at all).

Three uPlot charts (daily revenue, daily transaction count, top-5-drink
sold-qty trend) plus the same three tables Admin.tsx used to render inline
— those move here wholesale, Admin.tsx now just links to /stats instead of
fetching /admin/api/stats itself. The 'Statistik zurücksetzen' reset button
moves here too, gated on an actual admin session (checked separately from
whether /api/stats itself succeeded, since STATS_PUBLIC can make that true
for an anonymous viewer).

Chart lib is uPlot (~45kb) per mara's steer not to hand-roll this. Both
client and server build/typecheck clean; manually smoke-tested the auth
gate (401 unauthed, 200 after login) and the /stats route against a fresh
DB.

client/src/admin/Admin.tsx

@@ -27,9 +27,6 @@ async function errText(res: Response): Promise<string> {
 // same wire field). BarRow/stats shapes below are admin-only — not part
 // of the wire contract the tablet also consumes — so they stay local.
 interface BarRow extends Bar { drink_ids: number[] }
-interface Totals { bar_id: number; bar_name: string; tx_count: number; paid_cents: number; crew_count: number; pfand_returns: number }
-interface PerDrink { drink_id: number; drink_name: string; sold_qty: number }
-interface ByDay { day: string; tx_count: number; paid_cents: number; crew_count: number; pfand_returns: number }
 
 export function Admin() {
   const [authed, setAuthed] = useState<boolean | null>(null);
@@ -100,7 +97,10 @@ function Dashboard({ onLogout }: { onLogout: () => void }) {
           Abmelden
         </button>
       </div>
-      <Stats />
+      <div class="row" style="justify-content: space-between; align-items: center">
+        <h2 style="margin:0">Statistik</h2>
+        <a href="/stats">Statistik ansehen →</a>
+      </div>
       <Exports />
       <Drinks drinks={drinks} reload={reloadDrinks} />
       <Bars drinks={drinks} />
@@ -108,76 +108,6 @@ function Dashboard({ onLogout }: { onLogout: () => void }) {
   );
 }
 
-function fmtDay(day: string): string {
-  const [y, m, d] = day.split('-');
-  return `${d}.${m}.${y}`;
-}
-
-function Stats() {
-  const [data, setData] = useState<{ totals: Totals[]; per_drink: PerDrink[]; by_day: ByDay[] } | null>(null);
-  function reload() {
-    fetch('/admin/api/stats').then(j).then(setData).catch(e => alert(`Fehler beim Laden: ${e}`));
-  }
-  useEffect(reload, []);
-
-  async function reset() {
-    if (!confirm('Wirklich die gesamte Statistik (alle Transaktionen) unwiderruflich löschen?')) return;
-    await fetch('/admin/api/stats/reset', { method: 'POST' });
-    reload();
-  }
-
-  if (!data) return <p>Lade Statistik…</p>;
-  return (
-    <>
-      <div class="row" style="justify-content: space-between">
-        <h2 style="margin:0">Umsatz nach Tagen</h2>
-        <button class="danger" onClick={reset}>Statistik zurücksetzen</button>
-      </div>
-      <table>
-        <thead><tr><th>Tag</th><th>Transaktionen</th><th>Bezahlt</th><th>Crew-Transaktionen</th><th>Pfand zurück</th></tr></thead>
-        <tbody>
-          {data.by_day.length === 0 && <tr><td colSpan={5} class="muted">Noch keine Verkäufe</td></tr>}
-          {data.by_day.map(d => (
-            <tr key={d.day}>
-              <td>{fmtDay(d.day)}</td>
-              <td>{d.tx_count}</td>
-              <td>{formatCents(d.paid_cents)}</td>
-              <td>{d.crew_count}</td>
-              <td>{d.pfand_returns}</td>
-            </tr>
-          ))}
-        </tbody>
-      </table>
-      <h2>Umsatz pro Bar</h2>
-      <table>
-        <thead><tr><th>Bar</th><th>Transaktionen</th><th>Bezahlt</th><th>Crew-Transaktionen</th><th>Pfand zurück</th></tr></thead>
-        <tbody>
-          {data.totals.map(t => (
-            <tr key={t.bar_id}>
-              <td>{t.bar_name}</td>
-              <td>{t.tx_count}</td>
-              <td>{formatCents(t.paid_cents)}</td>
-              <td>{t.crew_count}</td>
-              <td>{t.pfand_returns}</td>
-            </tr>
-          ))}
-        </tbody>
-      </table>
-      <h2>Getränke</h2>
-      <table>
-        <thead><tr><th>Getränk</th><th>Verkauft</th></tr></thead>
-        <tbody>
-          {data.per_drink.map(d => (
-            <tr key={d.drink_id}>
-              <td>{d.drink_name}</td>
-              <td>{d.sold_qty ?? 0}</td>
-            </tr>
-          ))}
-        </tbody>
-      </table>
-    </>
-  );
-}
 
 function Exports() {
   return (