feat(auth): add row/size caps + streaming to export-user-data

- Add per-collection row cap (default 10k, env EXPORT_ROW_CAP) via Prisma
  take on all findMany calls
- Add total size cap (default 100MB, env EXPORT_SIZE_CAP_MB); throws
  PayloadTooLargeException (413) when exceeded
- Convert response to Node.js Readable stream piped via NestJS StreamableFile
  to avoid large in-memory buffers
- Export ExportUserDataResult interface (stream + truncated flag) from handler
- Update controller to set Content-Type/Content-Disposition headers and
  return StreamableFile
- Document EXPORT_ROW_CAP and EXPORT_SIZE_CAP_MB env vars in Swagger
- Extend tests: row-cap assertion (take arg), size-cap 413 path, stream assertions

Fixes GOO-223 (M-1 from GOO-200 audit).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

libs/contracts/events/schemas/payment.completed.schema.json

@@ -0,0 +1,32 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://goodgo.vn/schemas/events/payment.completed.schema.json",
+  "title": "payment.completed",
+  "description": "Emitted when a Payment aggregate transitions to SUCCEEDED after a verified gateway IPN (VNPay / MoMo / ZaloPay).",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "paymentId",
+    "orderId",
+    "userId",
+    "amount",
+    "currency",
+    "gateway",
+    "gatewayTransactionId",
+    "paidAt"
+  ],
+  "properties": {
+    "paymentId": { "type": "string", "minLength": 1 },
+    "orderId": { "type": "string", "minLength": 1 },
+    "userId": { "type": "string", "minLength": 1 },
+    "amount": {
+      "type": "string",
+      "pattern": "^-?\\d+(\\.\\d+)?$",
+      "description": "Decimal as string to preserve VND precision (no float rounding)."
+    },
+    "currency": { "type": "string", "enum": ["VND", "USD"] },
+    "gateway": { "type": "string", "enum": ["vnpay", "momo", "zalopay"] },
+    "gatewayTransactionId": { "type": "string", "minLength": 1 },
+    "paidAt": { "type": "string", "format": "date-time" }
+  }
+}