Add CEO-safe company portability flows

Expose CEO-scoped import/export preview and apply routes, keep safe imports non-destructive, add export preview-first UI behavior, and document the new portability workflows.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/__tests__/companies-route-path-guard.test.ts

@@ -15,6 +15,7 @@ vi.mock("../services/index.js", () => ({
   }),
   companyPortabilityService: () => ({
     exportBundle: vi.fn(),
+    previewExport: vi.fn(),
     previewImport: vi.fn(),
     importBundle: vi.fn(),
   }),