Unify past-sessions naming format

Format: YYYY-MM-DD-description.md
- 2026-01-19-infrastructure-deployment.md
- 2026-01-19-backend-api-implementation.md (in progress)

Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>

.agent/skills/vercel-react-best-practices/rules/js-batch-dom-css.md

@@ -0,0 +1,57 @@
+---
+title: Batch DOM CSS Changes
+impact: MEDIUM
+impactDescription: reduces reflows/repaints
+tags: javascript, dom, css, performance, reflow
+---
+
+## Batch DOM CSS Changes
+
+Avoid interleaving style writes with layout reads. When you read a layout property (like `offsetWidth`, `getBoundingClientRect()`, or `getComputedStyle()`) between style changes, the browser is forced to trigger a synchronous reflow.
+
+**Incorrect (interleaved reads and writes force reflows):**
+
+```typescript
+function updateElementStyles(element: HTMLElement) {
+  element.style.width = '100px'
+  const width = element.offsetWidth  // Forces reflow
+  element.style.height = '200px'
+  const height = element.offsetHeight  // Forces another reflow
+}
+```
+
+**Correct (batch writes, then read once):**
+
+```typescript
+function updateElementStyles(element: HTMLElement) {
+  // Batch all writes together
+  element.style.width = '100px'
+  element.style.height = '200px'
+  element.style.backgroundColor = 'blue'
+  element.style.border = '1px solid black'
+  
+  // Read after all writes are done (single reflow)
+  const { width, height } = element.getBoundingClientRect()
+}
+```
+
+**Better: use CSS classes**
+
+```css
+.highlighted-box {
+  width: 100px;
+  height: 200px;
+  background-color: blue;
+  border: 1px solid black;
+}
+```
+
+```typescript
+function updateElementStyles(element: HTMLElement) {
+  element.classList.add('highlighted-box')
+
+  const { width, height } = element.getBoundingClientRect()
+}
+```
+
+Prefer CSS classes over inline styles when possible. CSS files are cached by the browser, and classes provide better separation of concerns and are easier to maintain.