chore: Add agentic coding tooling

.crosslink/rules/typescript-react.md

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+### TypeScript/React Best Practices
+
+#### Component Structure
+- Use functional components with hooks
+- Keep components small and focused (< 200 lines)
+- Extract custom hooks for reusable logic
+- Use TypeScript interfaces for props
+
+```typescript
+// GOOD: Typed props with clear interface
+interface UserCardProps {
+    user: User;
+    onSelect: (id: string) => void;
+}
+
+const UserCard: React.FC<UserCardProps> = ({ user, onSelect }) => {
+    return (
+        <div onClick={() => onSelect(user.id)}>
+            {user.name}
+        </div>
+    );
+};
+```
+
+#### State Management
+- Use `useState` for local state
+- Use `useReducer` for complex state logic
+- Lift state up only when needed
+- Consider context for deeply nested prop drilling
+
+#### Performance
+- Use `React.memo` for expensive pure components
+- Use `useMemo` and `useCallback` appropriately (not everywhere)
+- Avoid inline object/function creation in render when passed as props
+
+#### Security
+- Never use `dangerouslySetInnerHTML` with user input
+- Sanitize URLs before using in `href` or `src`
+- Validate props at component boundaries