chore: vendor react-best-practices agent skill for cursor agents

Adds the Vercel skill under .agents with famapp path patterns.

Includes skills-lock.json pin.

.agents/skills/react-best-practices/rules/rendering-hydration-suppress-warning.md

@@ -0,0 +1,26 @@
+---
+title: Suppress Expected Hydration Mismatches
+impact: LOW-MEDIUM
+impactDescription: avoids noisy hydration warnings for known differences
+tags: rendering, hydration, ssr, nextjs
+---
+
+## Suppress Expected Hydration Mismatches
+
+In SSR frameworks (e.g., Next.js), some values are intentionally different on server vs client (random IDs, dates, locale/timezone formatting). For these _expected_ mismatches, wrap the dynamic text in an element with `suppressHydrationWarning` to prevent noisy warnings. Do not use this to hide real bugs. Don’t overuse it.
+
+**Incorrect (known mismatch warnings):**
+
+```tsx
+function Timestamp() {
+  return <span>{new Date().toLocaleString()}</span>;
+}
+```
+
+**Correct (suppress expected mismatch only):**
+
+```tsx
+function Timestamp() {
+  return <span suppressHydrationWarning>{new Date().toLocaleString()}</span>;
+}
+```