feat: QA restructure, browser ref staleness, eval efficiency metrics (v0.4.0) (#83)

* feat: browser ref staleness detection via async count() validation

resolveRef() now checks element count to detect stale refs after page
mutations (e.g. SPA navigation). RefEntry stores role+name metadata
for better diagnostics. 3 new snapshot tests for staleness detection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: qa-only skill, qa fix loop, plan-to-QA artifact flow

Add /qa-only (report-only, Edit tool blocked), restructure /qa with
find-fix-verify cycle, add {{QA_METHODOLOGY}} DRY placeholder for
shared methodology. /plan-eng-review now writes test-plan artifacts
to ~/.gstack/projects/<slug>/ for QA consumption.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: eval efficiency metrics — turns, duration, commentary across all surfaces

Add generateCommentary() for natural-language delta interpretation,
per-test turns/duration in comparison and summary output, judgePassed
unit tests, 3 new E2E tests (qa-only, qa fix loop, plan artifact).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: bump version and changelog (v0.4.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: update ARCHITECTURE, BROWSER, CONTRIBUTING, README for v0.4.0

- ARCHITECTURE: add ref staleness detection section, update RefEntry type
- BROWSER: add ref staleness paragraph to snapshot system docs
- CONTRIBUTING: update eval tool descriptions with commentary feature
- README: fix missing qa-only in project-local uninstall command

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add user-facing benefit descriptions to v0.4.0 changelog

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -42,6 +42,7 @@ gstack/
 │   ├── gen-skill-docs.test.ts    # Tier 1: generator quality (free, <1s)
 │   ├── skill-llm-eval.test.ts   # Tier 3: LLM-as-judge (~$0.15/run)
 │   └── skill-e2e.test.ts         # Tier 2: E2E via claude -p (~$3.85/run)
+├── qa-only/         # /qa-only skill (report-only QA, no fixes)
 ├── ship/            # Ship workflow skill
 ├── review/          # PR review skill
 ├── plan-ceo-review/ # /plan-ceo-review skill