Model Stammkapital/Grundkapital and Gesellschafter for the not-yet-needed legal forms

Mirrors the backend's new CompanySettings.shareCapital/generalPartners fields: rendered in the Impressum (AnbieterAngaben.tsx — new "Gesellschafter" section, Stammkapital line under Handelsregister, and the "Verantwortlich für den Inhalt" fallback now considers a general partner before falling back to sellerName) and wired into buildLegalFooterLines() for the invoice/email footer, same as registerCourt/registerNumber/managingDirector already were.

No visible change today (current legalForm is sole-proprietorship, neither field is set) — this is prep so a future legalForm change in company-settings updates the Impressum automatically instead of needing a manual Impressum edit at that point.

app/lib/emailTemplates.ts

@@ -102,6 +102,10 @@ export function buildLegalFooterLines(seller: CompanySettings | null): string[]
   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}`);
+  if (seller.shareCapital) lines.push(`Stammkapital: ${seller.shareCapital.toLocaleString("de-DE")} €`);
+  if (seller.generalPartners && seller.generalPartners.length > 0) {
+    lines.push(`Gesellschafter: ${seller.generalPartners.map((p) => p.name).join(", ")}`);
+  }
   return lines;
 }