test: add unit/component tests, E2E, and a11y + Lighthouse CI

[majicmaj]

What

Frontend testing from zero — the FE half of a testing initiative (Phases 1–3).

Unit / component (Vitest + RTL + MSW)

• src/test/ — Vitest setup, MSW server, renderWithProviders helper.
• DurationUtils / FilterEngine pure-logic tests (the filtering that decides which tasks a user sees).
• DurationInput component test — RTL + user-event + axe (a11y).

E2E (Playwright)

• Critical flows: signup and create → complete task, on desktop + mobile, auto-starting the Go backend + Vite dev server (playwright.config.js).

Accessibility (axe-core)

• e2e/a11y.spec.js scans the critical pages, gating on critical/serious with a known-issue baseline so it catches NEW regressions today and tightens as the shadcn migration lands.
• Added accessible labels to DurationInput (a real gap the axe test caught).

Lighthouse (advisory)

• lighthouserc.json + workflow — PWA/a11y/perf signal, all warn, never blocks.

CI

• Unit tests + build on every push; E2E + Lighthouse on PRs to develop; re-enabled lint as advisory.

Selectors survive the shadcn migration

Everything queries by accessible role/label/text, not MUI Joy DOM.

🤖 Generated with Claude Code

[KhyFee]

Strong testing bootstrap — Vitest/RTL/MSW + Playwright E2E + axe + advisory Lighthouse is a solid FE quality stack.

What’s working well

• Blocking unit tests in build.yml while keeping lint/Lighthouse advisory (continue-on-error) is a pragmatic ratchet.
• E2E limited to PRs targeting develop, backend pin, Playwright report upload, and chromium-only a11y scans (with an allowlist that you plan to shrink) are all good calls.
• Component-level vitest-axe on DurationInput catches issues earlier than full-page scans.

Review notes

1. Artifacts on failure: upload test-results/ (traces/screenshots) in e2e.yml with if: failure() in addition to the HTML report — much faster flake triage.
2. npm i vs npm ci: build/test jobs use npm i while e2e uses npm ci. Prefer npm ci everywhere in CI for lockfile-faithful installs.
3. Axe allowlist: keep the excluded rule IDs listed in TESTING.md with owners/tickets so the list doesn’t become permanent debt.
4. Backend pin: ref: develop on donetick/donetick can break FE PRs when backend moves. Consider pinning a SHA (or documenting that e2e failures may be cross-repo).

None of these are merge blockers — happy to see this land and ratchet lint to blocking once clean.