Add print cover fields and office profile

- Project settings gain siteAddress, workStage, projectLead and
  projectEditor (project.update-settings schema version 3, migration 0009);
  versions 2 and 1 stay executable and keep the current cover values.
  Snapshot schema 6 carries the fields; older versions upgrade with null.
- Global office profile (office name/address) next to the document logo:
  table document_branding_settings, PUT /api/document-branding/office,
  editable from the print view toolbar.
- Cover page reads all fields; empty values show the "[ergänzen]" marker.
  The Planstände editor column shows the project editor.
- Shared logo constants moved to a dependency-free module so the Next.js
  bundler can import them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/shared/constants/document-branding.ts

@@ -0,0 +1,9 @@
+export const documentLogoMimeTypes = [
+  "image/png",
+  "image/jpeg",
+  "image/svg+xml",
+] as const;
+
+export type DocumentLogoMimeType = (typeof documentLogoMimeTypes)[number];
+
+export const maxDocumentLogoBytes = 2 * 1024 * 1024;