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>

qa/templates/qa-report-template.md

@@ -72,6 +72,33 @@
 
 ---
 
+## Fixes Applied (if applicable)
+
+| Issue | Fix Status | Commit | Files Changed |
+|-------|-----------|--------|---------------|
+| ISSUE-NNN | verified / best-effort / reverted / deferred | {SHA} | {files} |
+
+### Before/After Evidence
+
+#### ISSUE-NNN: {title}
+**Before:** ![Before](screenshots/issue-NNN-before.png)
+**After:** ![After](screenshots/issue-NNN-after.png)
+
+---
+
+## Ship Readiness
+
+| Metric | Value |
+|--------|-------|
+| Health score | {before} → {after} ({delta}) |
+| Issues found | N |
+| Fixes applied | N (verified: X, best-effort: Y, reverted: Z) |
+| Deferred | N |
+
+**PR Summary:** "QA found N issues, fixed M, health score X → Y."
+
+---
+
 ## Regression (if applicable)
 
 | Metric | Baseline | Current | Delta |