feat: add MinIO object storage support

[ConradOsvik]

Summary

Implements MinIO S3-compatible object storage for file uploads, addressing the infrastructure requirements for handling user-generated content.

Changes

• Storage Service: Created src/lib/storage/ with S3-compatible client supporting upload, download, delete, and exists operations
• Context Integration: Added bucket to AppContext, accessible via c.get('ctx').bucket in all routes
• Docker Setup: Added MinIO service to dev and prod docker-compose configurations
• Environment Config: Added MinIO connection variables with sensible defaults
• Testing Support: Integrated MinIO testcontainer for isolated test environments

Usage Example

export default route().post('/', async (c) => {
  const { bucket } = c.get('ctx')
  
  // Upload a file
  const key = await bucket.upload('images/photo.jpg', fileBuffer, 'image/jpeg')
  
  // Download a file
  const file = await bucket.download('images/photo.jpg')
  
  // Check if exists
  const exists = await bucket.exists('images/photo.jpg')
  
  // Delete a file
  await bucket.delete('images/photo.jpg')
})

Test plan

• Type checking passes
• Linting passes
• MinIO testcontainer integration complete
• Run pnpm docker:dev to verify MinIO starts correctly
• Access MinIO console at http://localhost:9001
• Run integration tests to verify testcontainer setup

Closes #66