* feat(shared): add payment ladder and CSV domain package
Introduce @seahaven-ap/shared via npm workspaces so FE and future API share
payments-dashboard-compatible status ladders, pay-date helpers, and CSV headers.
* fix(web): build shared package before vite dev
Ensure fresh npm ci && npm run dev (and Playwright webServer) can resolve
@seahaven-ap/shared dist exports that are gitignored.
Rebuild the mock SPA shell to match the live Stampli product map (header, module rail, invoice/payment tabs, stubs) and add a Sea Haven brand flag for AP-23 cutover.