IMG-031: No Format Conversion

[murdore]

Summary

Unsupported formats (HEIC, TIFF) rejected instead of converted.

Fix

Implement format conversion using sharp library (HEIC→JPEG, TIFF→PNG).

Acceptance Criteria

• [ ] Implement format conversion using sharp
• [ ] Support HEIC→JPEG conversion
• [ ] Support TIFF→PNG conversion
• [ ] Configurable output format
• [ ] Add tests for format conversion

Estimated Effort: 8h