[ImagePicker] Add KDoc, defaults, and safe fallback handling

[AkshayAshokCode]

Polish the public API with developer-friendly documentation, safe defaults, and internal logging for edge failures.

Tasks:

Add KDoc to all public methods and configurations
Set smart defaults (e.g., source = GALLERY, crop = false)
Fallback to gallery if camera fails (optional)
Add internal logging tag for debugging
Ensure error messages are meaningful for developers