V2-S6: Integration verification, plan checklist update

- Update IMPLEMENTATION_PLAN_V2.md: WS-4 and WS-5 marked complete, WS-6 partial
  (cross-module wiring beyond report/hazard deferred), WS-7 complete (suite green)
- Full Pest suite verified green: 79 passed (167 assertions)
- Frontend rebuilt (tsc + vite) with no type errors, all new pages in manifest
