Merge feature/export-1: Datenexport (zip JSON+German CSVs) on /einstellungen + CI flake-cap [god-QA pending result-gate]

# Conflicts:
#	GerbilManager.Tests/GerbilManager.Tests.csproj
#	GerbilManagerWebAPI/Program.cs
#	gerbil-manager-web/src/App.tsx
#	gerbil-manager-web/src/components/AppShell.tsx
#	gerbil-manager-web/src/pages/EinstellungenPage.tsx

gerbil-manager-web/src/components/DatenexportCard.tsx

@@ -0,0 +1,21 @@
+/**
+ * EXPORT-1: Datenexport-Karte (auf /einstellungen) — lädt GET /export als Zip.
+ * Schlichter Anker-Download (kein fetch/Blob nötig); der Server setzt
+ * Content-Disposition mit Datumsdateinamen.
+ */
+import { API_BASE_URL } from '../api/client'
+import { de } from '../strings/de'
+
+export default function DatenexportCard() {
+  const t = de.pages.datenexport
+  return (
+    <section>
+      <h3>{t.title}</h3>
+      <p className="muted">{t.intro}</p>
+      <p className="muted">{t.photoNote}</p>
+      <a className="btn btn--primary" href={`${API_BASE_URL}/export`} download>
+        {t.button}
+      </a>
+    </section>
+  )
+}