feat: member portal Sprint 2 — digest history page and restore Digest/DigestConfig schema models

- Restore Digest + DigestConfig models to schema.prisma (wiped by prior git reset)
- Add Tenant.digestConfig / Tenant.digests relations
- GET /my/digest API endpoint (last 20 digests, truncated summary)
- BFF route /api/my/digest
- /my/digest page: digest cards with date, message count, summary preview
- Add Digest nav item to MemberShell sidebar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/api/my/digest/route.ts

@@ -0,0 +1,9 @@
+import { jsonResponse, memberApiFetch } from '../../../_lib/api';
+
+export const dynamic = 'force-dynamic';
+
+export async function GET(): Promise<Response> {
+  const res = await memberApiFetch('/my/digest');
+  const body = await res.json();
+  return jsonResponse(body, res.status);
+}