Use env variable for max file size limit

- Frontend: read VITE_MAX_FILE_SIZE_MB from env
- Update .env.example files with limits

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.env.example

@@ -12,3 +12,7 @@ S3_ACCESS_KEY=your-access-key
 S3_SECRET_KEY=your-secret-key
 S3_BUCKET_NAME=enigfm
 S3_REGION=ru-1
+
+# Limits
+MAX_FILE_SIZE_MB=10
+MAX_STORAGE_GB=90