Test: Image context fix — verify agents can see attached images

## Context
Commit d2df53c restored `crewai_files.ImageFile` + `input_files` in AgentFactory.

## Test steps
1. Attach an image in chat
2. Ask an agent to analyze it
3. Verify agent can see and describe the image

## Files changed
- `backend/attachment/processor.py`
- `backend/agents/factory.py`