Update environment variables and enhance Docker configurations for improved deployment

- Modified .env.portainer to include new environment variables for S3 private bucket URL, Nostr JWT secrets, and SendGrid options.
- Updated docker-compose.yml to support the new environment variables, enhancing service configurations.
- Added a seed content script to the backend package.json for initializing the database with sample data.
- Refactored helper functions to construct S3 URLs more robustly, accommodating potential missing configurations.
- Enhanced dev.sh script to seed the database if empty, ensuring content availability during development.

backend/src/common/helper.ts

@@ -22,7 +22,10 @@ export function getPublicS3Url(fileKey: string): string {
 }
 
 export function getPrivateS3Url(fileKey: string): string {
-  return `${process.env.S3_PRIVATE_BUCKET_URL}${encodeS3KeyForUrl(fileKey)}`;
+  const base =
+    process.env.S3_PRIVATE_BUCKET_URL ||
+    `${process.env.S3_ENDPOINT || 'http://localhost:9000'}/${process.env.S3_PRIVATE_BUCKET_NAME || 'indeedhub-private'}/`;
+  return `${base}${encodeS3KeyForUrl(fileKey)}`;
 }
 
 export function getTranscodedFileRoute(fileKey: string): string {