refactor: switch from Mailgun to AhaSend for email notifications

- Remove Mailgun dependencies
- Add AhaSend REST API integration
- Update configuration with AhaSend credentials
- Note: API returning 'invalid credentials' - may need AhaSend support verification

Credentials configured:
- Account ID: 8a14f9a5-6e6d-47c9-b5d6-a687265b36a3
- API Key: aha-sk-A0c9WOA8cs3RpvkAGwHOP9o6pHx-gLTUki1gSWVeC_6kd86-Npn077zta-rvg9oo

server/package.json

@@ -28,12 +28,11 @@
     "exifr": "^7.1.3",
     "express": "^4.21.1",
     "express-validator": "^7.2.0",
-    "form-data": "^4.0.4",
     "helmet": "^8.0.0",
     "json2csv": "^6.0.0-alpha.2",
-    "mailgun.js": "^12.1.1",
     "multer": "^1.4.5-lts.1",
     "node-cron": "^4.2.1",
+    "nodemailer": "^7.0.10",
     "redis": "^5.9.0",
     "zod": "^3.23.8"
   },
@@ -44,6 +43,7 @@
     "@types/multer": "^1.4.12",
     "@types/node": "^22.9.0",
     "@types/node-cron": "^3.0.11",
+    "@types/nodemailer": "^7.0.3",
     "prisma": "^5.22.0",
     "tsx": "^4.19.2",
     "typescript": "^5.6.3"