feat: add web frontend rules and design quality hook

rules/web/performance.md

@@ -0,0 +1,64 @@
+> This file extends [common/performance.md](../common/performance.md) with web-specific performance content.
+
+# Web Performance Rules
+
+## Core Web Vitals Targets
+
+| Metric | Target |
+|--------|--------|
+| LCP | < 2.5s |
+| INP | < 200ms |
+| CLS | < 0.1 |
+| FCP | < 1.5s |
+| TBT | < 200ms |
+
+## Bundle Budget
+
+| Page Type | JS Budget (gzipped) | CSS Budget |
+|-----------|---------------------|------------|
+| Landing page | < 150kb | < 30kb |
+| App page | < 300kb | < 50kb |
+| Microsite | < 80kb | < 15kb |
+
+## Loading Strategy
+
+1. Inline critical above-the-fold CSS where justified
+2. Preload the hero image and primary font only
+3. Defer non-critical CSS or JS
+4. Dynamically import heavy libraries
+
+```js
+const gsapModule = await import('gsap');
+const { ScrollTrigger } = await import('gsap/ScrollTrigger');
+```
+
+## Image Optimization
+
+- Explicit `width` and `height`
+- `loading="eager"` plus `fetchpriority="high"` for hero media only
+- `loading="lazy"` for below-the-fold assets
+- Prefer AVIF or WebP with fallbacks
+- Never ship source images far beyond rendered size
+
+## Font Loading
+
+- Max two font families unless there is a clear exception
+- `font-display: swap`
+- Subset where possible
+- Preload only the truly critical weight/style
+
+## Animation Performance
+
+- Animate compositor-friendly properties only
+- Use `will-change` narrowly and remove it when done
+- Prefer CSS for simple transitions
+- Use `requestAnimationFrame` or established animation libraries for JS motion
+- Avoid scroll handler churn; use IntersectionObserver or well-behaved libraries
+
+## Performance Checklist
+
+- [ ] All images have explicit dimensions
+- [ ] No accidental render-blocking resources
+- [ ] No layout shifts from dynamic content
+- [ ] Motion stays on compositor-friendly properties
+- [ ] Third-party scripts load async/defer and only when needed