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/types.ts

@@ -93,9 +93,18 @@ export interface ProjectDto {
   singlePhaseVoltageV: number;
   threePhaseVoltageV: number;
   enabledDistributionBoardSupplyTypes: DistributionBoardSupplyType[];
+  siteAddress: string | null;
+  workStage: string | null;
+  projectLead: string | null;
+  projectEditor: string | null;
   currentRevision: number;
 }
 
+export interface OfficeProfileDto {
+  officeName: string | null;
+  officeAddress: string | null;
+}
+
 export interface ProjectHistoryStateDto {
   projectId: string;
   currentRevision: number;