Enable admins and directors to send invoices via webhook

Introduce a new backend route `/api/reconciliation/send-invoice-webhook` to proxy invoice data to external webhooks, converting files to base64 and handling CORS issues.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 1e4433b5-47ab-464c-b663-fea2e53367dd
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 6f3c3694-5a67-4b47-b27c-af49da7ad447
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/1957c339-2757-4d1f-8e92-e9f71a1ce58e/1e4433b5-47ab-464c-b663-fea2e53367dd/LXHtbOp

package.json

@@ -43,6 +43,7 @@
     "@radix-ui/react-tooltip": "^1.2.0",
     "@tanstack/react-query": "^5.60.5",
     "@types/bcrypt": "^6.0.0",
+    "@types/form-data": "^2.2.1",
     "@types/memoizee": "^0.4.12",
     "@types/node-fetch": "^2.6.13",
     "@types/pg": "^8.15.4",
@@ -60,6 +61,7 @@
     "express": "^4.21.2",
     "express-rate-limit": "^7.5.1",
     "express-session": "^1.18.1",
+    "form-data": "^4.0.4",
     "framer-motion": "^11.13.1",
     "iconv-lite": "^0.6.3",
     "input-otp": "^1.4.2",