feat(cli): mentions target user

src/lib/normalize-handle.ts

@@ -0,0 +1,13 @@
+export function normalizeHandle(input?: string | null): string | null {
+  const raw = (input ?? '').trim();
+  if (!raw) return null;
+
+  const withoutAt = raw.startsWith('@') ? raw.slice(1) : raw;
+  const handle = withoutAt.trim();
+  if (!handle) return null;
+
+  // X/Twitter handles are traditionally max 15 chars; keep strict to avoid surprising queries.
+  if (!/^[A-Za-z0-9_]{1,15}$/.test(handle)) return null;
+
+  return handle;
+}