[OPER-QA-12] E2E Fiesta UAT loop test — create project, invite, assign, complete, coverage updates

feature_id: FEAT-studio-qa-projects

## Context

End-to-end Playwright test that walks the whole assignment loop from a real Studio operator's perspective. Runs against the Neon preview branch. This is the acceptance test for "Ana + Hannah at Fiesta receive assigned QA tasks in Portico and complete them."

Failing this test blocks any release of the QA product line to a real tenant.

## Acceptance Criteria

- `e2e/qa-fiesta-uat-loop.spec.ts` performs: (1) sign in as operator; (2) create TestProject 'Fiesta Wave 1'; (3) add 3 phases; (4) invite [REDACTED-EMAIL] (role: RUNNER) via magic link; (5) accept invite in second browser context; (6) assign 5 TestCases across phases; (7) resolve phase 1 to IN_PROGRESS; (8) run first assignment as ana (start, evidence, PASSED); (9) verify CoverageCell went GREEN for that (feature, kind); (10) sign back in as operator, verify Bug Board empty
- Test tolerates real magic-link email via Postmark test API or in-DB peek
- Runs against `neon-preview` branch, cleans up TestProject + members + assignments in afterAll hook
- CI job `e2e-qa-loop` on every PR that touches `packages/qa/**`, `apps/web/src/app/(app)/[team]/qa/**`, or `apps/web/src/app/api/studio/[team]/qa/**`