feat: extract shared payment utilities from rubgram

Move checkSlip into a shared lib/payment module so the donate page can reuse it without duplicating SlipOK API logic.

lib/payment.ts

@@ -0,0 +1,31 @@
+import { SlipokResponse } from "@/app/(ui)/rubgram/api";
+
+const { SLIPOK_API_URL, SLIPOK_API_KEY } = process.env as Record<
+  string,
+  string
+>;
+
+export async function checkSlip(
+  buffer: Buffer<ArrayBuffer>,
+  type: string,
+  amount: number,
+): Promise<SlipokResponse> {
+  const response = await fetch(SLIPOK_API_URL, {
+    method: "POST",
+    headers: {
+      "x-authorization": SLIPOK_API_KEY,
+    },
+    body: (() => {
+      const formData = new FormData();
+      formData.append("files", new Blob([buffer], { type }), "image");
+      formData.append("amount", amount.toString());
+      // formData.append("log", "true"); // no log cause im logging myself
+      return formData;
+    })(),
+  });
+
+  const data = await response.json();
+
+  // if (!response.ok) throw data;
+  return data;
+}