feat: add 6 gap-closing skills — browser QA, design system, product lens, canary watch, benchmark, safety guard

Closes competitive gaps with gstack:
- browser-qa: automated visual testing via browser MCP
- design-system: generate, audit, and detect AI slop in UI
- product-lens: product diagnostic, founder review, feature prioritization
- canary-watch: post-deploy monitoring with alert thresholds
- benchmark: performance baseline and regression detection
- safety-guard: prevent destructive operations in autonomous sessions

skills/browser-qa/SKILL.md

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+# Browser QA — Automated Visual Testing & Interaction
+
+## When to Use
+
+- After deploying a feature to staging/preview
+- When you need to verify UI behavior across pages
+- Before shipping — confirm layouts, forms, interactions actually work
+- When reviewing PRs that touch frontend code
+- Accessibility audits and responsive testing
+
+## How It Works
+
+Uses the browser automation MCP (claude-in-chrome, Playwright, or Puppeteer) to interact with live pages like a real user.
+
+### Phase 1: Smoke Test
+```
+1. Navigate to target URL
+2. Check for console errors (filter noise: analytics, third-party)
+3. Verify no 4xx/5xx in network requests
+4. Screenshot above-the-fold on desktop + mobile viewport
+5. Check Core Web Vitals: LCP < 2.5s, CLS < 0.1, INP < 200ms
+```
+
+### Phase 2: Interaction Test
+```
+1. Click every nav link — verify no dead links
+2. Submit forms with valid data — verify success state
+3. Submit forms with invalid data — verify error state
+4. Test auth flow: login → protected page → logout
+5. Test critical user journeys (checkout, onboarding, search)
+```
+
+### Phase 3: Visual Regression
+```
+1. Screenshot key pages at 3 breakpoints (375px, 768px, 1440px)
+2. Compare against baseline screenshots (if stored)
+3. Flag layout shifts > 5px, missing elements, overflow
+4. Check dark mode if applicable
+```
+
+### Phase 4: Accessibility
+```
+1. Run axe-core or equivalent on each page
+2. Flag WCAG AA violations (contrast, labels, focus order)
+3. Verify keyboard navigation works end-to-end
+4. Check screen reader landmarks
+```
+
+## Output Format
+
+```markdown
+## QA Report — [URL] — [timestamp]
+
+### Smoke Test
+- Console errors: 0 critical, 2 warnings (analytics noise)
+- Network: all 200/304, no failures
+- Core Web Vitals: LCP 1.2s ✓, CLS 0.02 ✓, INP 89ms ✓
+
+### Interactions
+- [✓] Nav links: 12/12 working
+- [✗] Contact form: missing error state for invalid email
+- [✓] Auth flow: login/logout working
+
+### Visual
+- [✗] Hero section overflows on 375px viewport
+- [✓] Dark mode: all pages consistent
+
+### Accessibility
+- 2 AA violations: missing alt text on hero image, low contrast on footer links
+
+### Verdict: SHIP WITH FIXES (2 issues, 0 blockers)
+```
+
+## Integration
+
+Works with any browser MCP:
+- `mChild__claude-in-chrome__*` tools (preferred — uses your actual Chrome)
+- Playwright via `mcp__browserbase__*`
+- Direct Puppeteer scripts
+
+Pair with `/canary-watch` for post-deploy monitoring.