feat(expo): add useChatUnread hook for unread count polling

xtablo-expo/hooks/chatUnread.ts

@@ -0,0 +1,31 @@
+import { useQuery } from "@tanstack/react-query";
+import { useAuthStore } from "@/stores/auth";
+import { UnreadCount } from "@/types/chat.types";
+
+const CHAT_API_BASE = process.env.EXPO_PUBLIC_CHAT_API_URL as string;
+
+export function useChatUnread() {
+  const session = useAuthStore((state) => state.session);
+  const token = session?.access_token;
+
+  const { data, refetch } = useQuery({
+    queryKey: ["chat-unread"],
+    queryFn: async (): Promise<UnreadCount[]> => {
+      const res = await fetch(`${CHAT_API_BASE}/chat/unread`, {
+        headers: { Authorization: `Bearer ${token}` },
+      });
+      if (!res.ok) return [];
+      const json = (await res.json()) as { unread: UnreadCount[] };
+      return json.unread;
+    },
+    enabled: !!token,
+    refetchInterval: 30_000,
+  });
+
+  return {
+    unreadCounts: data ?? [],
+    getUnreadCount: (channelId: string) =>
+      data?.find((u) => u.channel_id === channelId)?.unread_count ?? 0,
+    refetch,
+  };
+}