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/invoicePdf.tsx

@@ -119,6 +119,14 @@ export type InvoiceSeller = {
   vatId: string;
   taxRatePercent: number;
   bankDetails?: string | null;
+  // Pflichtangaben in Geschäftsbriefen for registered legal forms (§37a
+  // HGB / §35a GmbHG) — optional because a sole proprietorship (the
+  // default legalForm in company-settings) has neither. See
+  // buildLegalFooterLines() in emailTemplates.ts for the same fields'
+  // equivalent treatment in the email footer.
+  registerCourt?: string | null;
+  registerNumber?: string | null;
+  managingDirector?: string | null;
 };
 
 // Used only by /company-settings-preview's Live Preview — a fixed sample
@@ -305,6 +313,8 @@ export function InvoiceDocument({ order, seller }: { order: InvoiceOrder; seller
           <Text>
             {seller.sellerName} · {seller.sellerStreet}, {seller.sellerZip} {seller.sellerCity} · {seller.sellerEmail} · USt-IdNr.{" "}
             {seller.vatId}
+            {seller.registerCourt && seller.registerNumber ? ` · ${seller.registerCourt} · ${seller.registerNumber}` : ""}
+            {seller.managingDirector ? ` · Geschäftsführung: ${seller.managingDirector}` : ""}
           </Text>
           {seller.bankDetails ? <Text style={{ marginTop: 4 }}>Bankverbindung (für Überweisung): {seller.bankDetails}</Text> : null}
         </View>