Add dotenv support and bulk SMS endpoint

- Integrated dotenv for environment variable management.
- Updated queueWorker to use WORKER_INTERVAL from .env or default to 5 seconds.
- Added a new bulk SMS endpoint to queue multiple messages in a single request, with validation and transaction handling.
- Updated package.json and package-lock.json to include dotenv dependency.

package.json

@@ -10,6 +10,7 @@
   "author": "",
   "license": "ISC",
   "dependencies": {
+    "dotenv": "^17.4.2",
     "express": "^4.18.2",
     "socket.io": "^4.7.4",
     "sqlite3": "^6.0.1"