test(playwright-config): bring playwright.config.js into the coverage report

[hivecommons-hive]

Test Improvement

Adds tests/playwright-config.test.mjs.

playwright.config.js was the only executable JavaScript file at the repository
root missing from the npm run test:unit:coverage report. docusaurus.config.js
and sidebars.js are both reported at 100.00 / 100.00 because
tests/site-config.test.mjs imports them; nothing imported
playwright.config.js, so Node never instrumented it and the
test:unit:coverage:check gate could not see it at all.

The new test follows the loadConfig(env) cache-busting pattern already
established in tests/site-config.test.mjs, re-importing the config under
controlled environment variables so each module-scope branch is observed:

• E2E_PORT default (3000) and override, asserted across all three places the
  port is interpolated — use.baseURL, webServer.url, and
  webServer.command. Drift between them would hang the suite at startup.
• CI set, unset, and empty-string, covering the !!/ternary boundary that
  simultaneously switches forbidOnly, retries, reporter, and
  webServer.reuseExistingServer.
• fullyParallel and trace: 'retain-on-failure'.
• Exactly one project, carrying the Desktop Chrome device descriptor.
• testDir names a directory that exists and actually contains .spec.js
  files, so moving or renaming the spec directory fails loudly instead of
  reporting zero tests and exiting successfully.
• webServer.timeout is a positive, bounded number.

Result

playwright.config.js now appears in the report at 100.00 / 100.00, and src files rises from 5401/5401 to 5432/5432 lines. npm run test:unit:coverage:check (--check 97 --check-source 99) passes, as does
npx prettier --check on the new file.

No production code is touched — the config itself is unchanged.

Scope / overlap

Adds one new test file and nothing else. Disjoint from the e2e specs in #723 and
#729, the shared sandbox helpers in #727, the coverage-report tool in #702 and
#719, the harness files in #706 and #708, and every scripts/ module claimed by
#678, #680, #686, #688, and #693.

Related Issue

Closes #732

---

Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88

[hivecommons-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will automatically remove the hold label once current policy no longer requires a level hold for "quality". If this is an outreach PR, a human must review it and remove the label.

[mrbobbytables]

Superseded by #750, which consolidates this and 14 other test-only coverage PRs into a single reviewable change (commit cherry-picked unmodified, authorship and DCO preserved).