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/canary-watch/SKILL.md

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+# Canary Watch — Post-Deploy Monitoring
+
+## When to Use
+
+- After deploying to production or staging
+- After merging a risky PR
+- When you want to verify a fix actually fixed it
+- Continuous monitoring during a launch window
+- After dependency upgrades
+
+## How It Works
+
+Monitors a deployed URL for regressions. Runs in a loop until stopped or until the watch window expires.
+
+### What It Watches
+
+```
+1. HTTP Status — is the page returning 200?
+2. Console Errors — new errors that weren't there before?
+3. Network Failures — failed API calls, 5xx responses?
+4. Performance — LCP/CLS/INP regression vs baseline?
+5. Content — did key elements disappear? (h1, nav, footer, CTA)
+6. API Health — are critical endpoints responding within SLA?
+```
+
+### Watch Modes
+
+**Quick check** (default): single pass, report results
+```
+/canary-watch https://myapp.com
+```
+
+**Sustained watch**: check every N minutes for M hours
+```
+/canary-watch https://myapp.com --interval 5m --duration 2h
+```
+
+**Diff mode**: compare staging vs production
+```
+/canary-watch --compare https://staging.myapp.com https://myapp.com
+```
+
+### Alert Thresholds
+
+```yaml
+critical:  # immediate alert
+  - HTTP status != 200
+  - Console error count > 5 (new errors only)
+  - LCP > 4s
+  - API endpoint returns 5xx
+
+warning:   # flag in report
+  - LCP increased > 500ms from baseline
+  - CLS > 0.1
+  - New console warnings
+  - Response time > 2x baseline
+
+info:      # log only
+  - Minor performance variance
+  - New network requests (third-party scripts added?)
+```
+
+### Notifications
+
+When a critical threshold is crossed:
+- Desktop notification (macOS/Linux)
+- Optional: Slack/Discord webhook
+- Log to `~/.claude/canary-watch.log`
+
+## Output
+
+```markdown
+## Canary Report — myapp.com — 2026-03-23 03:15 PST
+
+### Status: HEALTHY ✓
+
+| Check | Result | Baseline | Delta |
+|-------|--------|----------|-------|
+| HTTP | 200 ✓ | 200 | — |
+| Console errors | 0 ✓ | 0 | — |
+| LCP | 1.8s ✓ | 1.6s | +200ms |
+| CLS | 0.01 ✓ | 0.01 | — |
+| API /health | 145ms ✓ | 120ms | +25ms |
+
+### No regressions detected. Deploy is clean.
+```
+
+## Integration
+
+Pair with:
+- `/browser-qa` for pre-deploy verification
+- Hooks: add as a PostToolUse hook on `git push` to auto-check after deploys
+- CI: run in GitHub Actions after deploy step