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/js-early-exit.md

@@ -0,0 +1,50 @@
+---
+title: Early Return from Functions
+impact: LOW-MEDIUM
+impactDescription: avoids unnecessary computation
+tags: javascript, functions, optimization, early-return
+---
+
+## Early Return from Functions
+
+Return early when result is determined to skip unnecessary processing.
+
+**Incorrect (processes all items even after finding answer):**
+
+```typescript
+function validateUsers(users: User[]) {
+  let hasError = false;
+  let errorMessage = "";
+
+  for (const user of users) {
+    if (!user.email) {
+      hasError = true;
+      errorMessage = "Email required";
+    }
+    if (!user.name) {
+      hasError = true;
+      errorMessage = "Name required";
+    }
+    // Continues checking all users even after error found
+  }
+
+  return hasError ? { valid: false, error: errorMessage } : { valid: true };
+}
+```
+
+**Correct (returns immediately on first error):**
+
+```typescript
+function validateUsers(users: User[]) {
+  for (const user of users) {
+    if (!user.email) {
+      return { valid: false, error: "Email required" };
+    }
+    if (!user.name) {
+      return { valid: false, error: "Name required" };
+    }
+  }
+
+  return { valid: true };
+}
+```