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/frontend/print/print-document.css

@@ -1,6 +1,6 @@
-/* Print view (Seitenansicht) in the provisional kbp corporate design.
-   Colors are derived from the kbp logo and presentation material and will be
-   replaced by the official CD specification; change them only here.
+/* Print view (Seitenansicht) in the kbp corporate design. Colors are
+   derived from the kbp logo and presentation material; change them only
+   here.
    All selectors are scoped to .print-view. The @page rules (format, margins,
    page numbers) are injected by the print page because they need project
    data. */
@@ -113,6 +113,9 @@
   color: var(--pd-accent);
   font-weight: bold;
 }
+.pd-multiline {
+  white-space: pre-line;
+}
 .pd-logo {
   display: block;
   max-width: 100%;