ci(test): aggregate coverage via Codecov

[JohnRDOrazio]

Background

With #86 / #87 / #88 merged (closing #63), we now have three independent test runners producing coverage data:

• Vitest — lib/wordpress/* (Next.js data layer). Already supports npm run test:coverage (v8 provider).
• PHPUnit + Brain Monkey — cdcf-redis-translations plugin and cdcf-headless theme /cdcf/v1/* REST handlers.
• bats-core — scripts/cdcf_queue_worker.lib.sh queue-worker helpers.

Each runner is wired as a non-blocking CI check today (see workflows: `test-nextjs.yml`, `test-wordpress.yml`, `test-worker.yml`). There is no central place to view total coverage or see PR-level deltas.

Suggested scope

Phase 1 — Vitest + PHPUnit

• Add Codecov upload step to `test-nextjs.yml` (lcov / json from v8 reporter)
• Add Codecov upload step to `test-wordpress.yml` for both composer trees (clover from PHPUnit)
• Add a top-level `codecov.yml` with non-blocking thresholds (matches the current "tests don't gate merges" posture). Suggested:
  • `coverage.status.project: informational: true`
  • `coverage.status.patch: informational: true`
  • Per-flag carryforward so a PR that only touches one tree doesn't reset the others
• Use Codecov flags (`nextjs`, `wordpress-plugin`, `wordpress-theme`) so each tree is reported separately
• Add a Codecov badge to README under the existing PR Build badge

Phase 2 — bats worker (later)

• Wrap `scripts/tests/bats/bin/bats` with kcov to emit cobertura-compatible coverage
• Add to `test-worker.yml` with the `worker` flag
• Defer until Phase 1 is stable — kcov on Ubuntu runners is fiddlier than the Vitest/PHPUnit upload paths

Out of scope here

• Making coverage gating mandatory (current policy: tests are non-blocking)
• Coverage for components, E2E paths, or anything not already exercised by the existing suites

Why now

Three runners means three places to look. Codecov gives a single PR comment with per-flag deltas, which is the lightest-weight win available — no behavior change, just visibility. Free for public repos.

Related

• feat: add test suites for Next.js frontend and WordPress theme/plugins #63 — test suites (closed)
• feat(test): Vitest suite for lib/wordpress/* (pilot for #63) #86, feat(test): bats-core suite for cdcf_queue_worker.sh (Refs #63) #87, feat(test): PHPUnit + Brain Monkey suites for plugin and theme (Refs #63) #88 — the test PRs that produced the coverable code

[JohnRDOrazio]

Phase 2 wired in #101 (kcov + cobertura → worker flag). Both phases of the rollout plan are now in place:

• Phase 1 (ci(test): aggregate Vitest + PHPUnit coverage via Codecov (Phase 1, refs #91) #92) — Vitest + PHPUnit ×2 upload, codecov.yml, README badge
• Phase 2 (ci(test): bats coverage via kcov (Phase 2 of #91) #101) — bats instrumented with kcov, worker flag

Per-flag coverage (post-#101): nextjs 68%, wordpress-plugin 52%, wordpress-theme 1%, worker ~45%. The theme number is what's dragging the aggregate down; tracked separately in #100 (expand PHPUnit coverage of functions.php).