Add legalForm-driven Pflichtangaben (register court/number, managing director)

Mirrors the Payload backend's new company-settings.legalForm field: when
present, registerCourt/registerNumber/managingDirector now appear in the
email footer (buildLegalFooterLines) and both invoice PDF footers,
matching §37a HGB / §35a GmbHG requirements for registered legal forms.
A sole proprietorship (the default) renders identically to before —
these fields are only appended when actually set.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/emailTemplates.ts

@@ -80,10 +80,13 @@ export const DEFAULT_LEGAL_FOOTER_LINES: string[] = [
 // plus VAT ID once assigned) — not just a friendly "brand · email" line.
 // Built from the same company-settings fields the invoice PDFs already
 // render (app/lib/invoicePdf.tsx), so there is exactly one source of truth
-// for this business's legal identity. If company-settings ever grows a
-// Handelsregister court/number or Geschäftsführer field (needed once this
-// business is a registered legal form rather than a sole proprietorship),
-// add those lines here too.
+// for this business's legal identity.
+//
+// registerCourt/registerNumber/managingDirector are conditionally required
+// on the Payload side (CompanySettings.ts, gated by legalForm) — only
+// appended here when actually present, so a sole proprietorship's footer
+// stays exactly as short as before this field set existed. Keep this in
+// sync with the Payload backend's own copy in src/lib/sellerInfo.ts.
 export function buildLegalFooterLines(seller: CompanySettings | null): string[] {
   if (!seller) return DEFAULT_LEGAL_FOOTER_LINES;
   const lines = [
@@ -93,6 +96,8 @@ export function buildLegalFooterLines(seller: CompanySettings | null): string[]
     `E-Mail: ${seller.sellerEmail}`,
   ];
   if (seller.vatId) lines.push(`USt-IdNr.: ${seller.vatId}`);
+  if (seller.registerCourt && seller.registerNumber) lines.push(`${seller.registerCourt} · ${seller.registerNumber}`);
+  if (seller.managingDirector) lines.push(`Geschäftsführung: ${seller.managingDirector}`);
   return lines;
 }