Gutschriften Phase 3a: Firmenstammdaten (Absender) fuer PDF/ZUGFeRD

Neues CompanyProfile-Modell (Einzel-Zeile) + Migration (IF NOT EXISTS):
Firmenname, Anschrift, USt-IdNr, Steuernummer, Handelsregister,
Geschaeftsfuehrer, Kontakt, IBAN/BIC/Bank. Fliesst spaeter in
Gutschrift-PDF + ZUGFeRD-Verkaeuferdaten ein.

Backend: Service (getOrCreate/update mit Feld-Whitelist), Controller,
Routes GET/PUT /api/company-profile (settings:read/update), auditiert.

Frontend: Settings-Seite 'Firmenstammdaten (Absender)'
(/settings/company-profile) mit Firma/Anschrift, Steuer/Register,
Kontakt/Bank. Typ + companyProfileApi + Menue-Eintrag.

Phase 3b (PDF + ZUGFeRD-Erzeugung) folgt darauf auf.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -24,6 +24,7 @@ import ContractDurationList from './pages/settings/ContractDurationList';
 import ProviderList from './pages/settings/ProviderList';
 import ContractCategoryList from './pages/settings/ContractCategoryList';
 import CreditNoteNumberRange from './pages/settings/CreditNoteNumberRange';
+import CompanyProfileSettings from './pages/settings/CompanyProfileSettings';
 import ViewSettings from './pages/settings/ViewSettings';
 import PortalSettings from './pages/settings/PortalSettings';
 import DeadlineSettings from './pages/settings/DeadlineSettings';
@@ -224,6 +225,7 @@ function App() {
         <Route path="settings/providers" element={<ProviderList />} />
         <Route path="settings/contract-categories" element={<ContractCategoryList />} />
         <Route path="settings/credit-note-number-range" element={<CreditNoteNumberRange />} />
+        <Route path="settings/company-profile" element={<CompanyProfileSettings />} />
         <Route path="settings/view" element={<ViewSettings />} />
         <Route path="settings/portal" element={<PortalSettings />} />
         <Route path="settings/deadlines" element={<DeadlineSettings />} />