feat: add BullMQ queue infrastructure and frontend job status hook

- apps/Backend/src/queue/: connection, queues, workers, processors
- apps/Frontend/src/hooks/use-job-status.ts: WebSocket job progress hook
- apps/Frontend/src/lib/socket.ts: shared Socket.IO singleton

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Backend/src/queue/processors/ocrProcessor.ts

@@ -0,0 +1,42 @@
+/**
+ * Processor for "ocr" jobs.
+ * Calls the PaymentOCR Python service with the uploaded files.
+ */
+import axios from "axios";
+import FormData from "form-data";
+
+const OCR_BASE_URL =
+  process.env.OCR_SERVICE_BASE_URL || "http://localhost:5003";
+
+export interface OcrProcessorInput {
+  files: { originalname: string; bufferBase64: string; mimetype: string }[];
+}
+
+export async function runOcrProcessor(
+  input: OcrProcessorInput
+): Promise<any[]> {
+  const { files } = input;
+
+  const form = new FormData();
+  for (const f of files) {
+    const buf = Buffer.from(f.bufferBase64, "base64");
+    form.append("files", buf, {
+      filename: f.originalname,
+      contentType: f.mimetype,
+      knownLength: buf.length,
+    });
+  }
+
+  const resp = await axios.post<{ rows: any[] }>(
+    `${OCR_BASE_URL}/extract/json`,
+    form,
+    {
+      headers: form.getHeaders(),
+      maxBodyLength: Infinity,
+      maxContentLength: Infinity,
+      timeout: 180_000, // OCR can be heavy; 3-minute limit
+    }
+  );
+
+  return resp.data?.rows ?? [];
+}