feat: improve file upload validation #8

Medium Priority#

Location: src/index.ts:1879-1903

Issues:#

• File extension check but no MIME type verification
• No malware scanning
• No image/audio validation beyond size
• Filename not sanitized before storage

Impact#

Malicious file uploads, path traversal attempts

Fix Time#

~1 hour

Recommendation#

Add MIME type validation, sanitize filenames, validate file headers

From LAUNCH_REVIEW.md Issue #18