[P6.8.5] Rewrite Playwright browser E2E suite against current Phase-3+ UI

[frankbria]

Context

Follow-up from #647 (P6.5.2), which formally deferred the two disabled Playwright browser-level E2E jobs (e2e-smoke-tests, e2e-frontend-tests) rather than re-enabling them.

Why they were deferred, not re-enabled: the entire tests/e2e/*.spec.ts suite targets a /projects/[id] route architecture that no longer exists. Evidence (as of 2026-06-15):

• 19 of 19 spec files reference /projects; specs page.goto('${FRONTEND_URL}/projects/${PROJECT_ID}') 36+ times, plus /signup, /projects/1.
• Current UI is workspace-based: blockers, costs, execution, login, prd, proof, review, sessions, settings, tasks — no /projects, /dashboard, /metrics, /signup, /git-visualization, /checkpoint pages.
• tests/e2e/E2E_TEST_AUDIT.md (dated 2026-01-09) describes login redirecting to /projects — stale.

Against the current UI these tests fail immediately (404 → login redirect), so re-enabling as-is would only create a perpetually-red job. The suite needs a rewrite, not a fix.

Scope

Rewrite the browser E2E suite to match the current Phase-3+ UI and auth model:

• New auth flow: /login (JWT in localStorage) per Enforce authentication across the v2 API (routers, WS/SSE, and web-UI login) #336; SSE/WS ?token= query auth.
• New page structure: /, /prd, /tasks, /execution, /execution/[taskId], /blockers, /proof, /proof/[req_id], /review, /sessions, /sessions/[id], /settings, /costs.
• Replace /projects/[id]-based navigation and /signup flows.
• Re-wire the CI jobs (smoke on PR, full on schedule) and into test-summary once green.
• Re-enable the nightly schedule: cron in .github/workflows/test.yml when the suite is stable.

Acceptance criteria

• Playwright smoke suite passes against the current UI and runs on PRs.
• Full browser suite runs on a schedule (nightly) and passes.
• Jobs wired into test-summary; nightly schedule: cron re-enabled.
• tests/e2e/E2E_TEST_AUDIT.md refreshed (or removed) to match the new suite.

[coderabbitai]

🔗 Related PRs

#36 - fix: Add npm install step for E2E test dependencies [merged]
#93 - fix(e2e): Fix dashboard and metrics tests for tab-based UI rendering [merged]
#188 - feat(e2e): Add comprehensive error monitoring and strict verification [merged]
#191 - feat(e2e): Enable conditional tests and fix discovery startup [merged]
#681 - ci(frontend): add npm run build + re-enable frontend lint (#646) [closed]

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