Implement comprehensive S3 error handling with retry logic

[Asi0Flammeus]

Description

The current S3 integration lacks comprehensive error handling, which could lead to poor user experience and potential security vulnerabilities.

Problems

• Missing specific S3 error code handling (NoSuchKey, AccessDenied, etc.)
• No retry logic for transient S3 failures
• Generic error messages that don't help users understand what went wrong

Requirements

• Handle specific S3 error codes with appropriate HTTP status codes
• Implement exponential backoff retry logic for transient failures
• Add proper logging for S3 operations
• Return user-friendly error messages
• Add timeout handling for S3 operations

Acceptance Criteria

• S3 errors return appropriate HTTP status codes (404 for NoSuchKey, 403 for AccessDenied)
• Retry logic with exponential backoff for transient failures
• Clear error messages for users
• Comprehensive logging for debugging

Related

• Addresses security concerns from PR Create API endpoints for contribute app #22
• Improves reliability of S3 operations in /translate/*_s3 endpoints

Priority

High - Security and reliability issue