Mounts AdminAuth (HTTP Basic on /admin/*) and adds two route groups:
- Admin (/admin/invoices): list, new form, create, show, toggle-paid.
POST /admin/invoices builds the Invoice, renders the PDF, uploads to
MinIO, then persists the row with the resulting pdf_key.
- Public (/i/:uuid): an HTML landing page showing client name, number,
total, and status badge, plus /i/:uuid/pdf which 302s to a short-lived
MinIO presigned URL. Anyone with the UUID can fetch the PDF — that's
the whole point of the link-based delivery.
The Invoice model is required only when DATABASE_URL is set, so the
contact-form site still boots in dev without Postgres. Invoicing routes
return 503 in that mode rather than crashing on first request.
