InvoiceOrder/CorrectionInvoiceOrder gain an optional order-level
kleinunternehmer flag, snapshotted per order (same pattern as vatExempt)
so a later toggle of the tenant's setting never rewrites an
already-issued invoice. Takes precedence over vatExempt.
- Visual PDF: "enthält X% MwSt." becomes the §19 UStG notice.
- E-invoice XML: new UNTDID 5305 category "E" with a free-text exemption
reason (no VATEX code — §19 UStG has none, BR-E-10 allows text alone).
- New Mustang CI fixture + buildEInvoiceData unit test for the "E" path.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Adds a Gitea Actions workflow that generates realistic e-invoice fixtures (multi-VAT-rate original invoice, Storno, Gutschrift) and validates them against the reference Mustang validator on every push, catching a broken EN16931 mapping before it reaches production instead of relying on manual spot-checks.
Marco