feat(aionrs): inline image attachments for Aion CLI

[s-yanev]

Summary

This PR enables image attachments to work with the Aion CLI backend by converting attached image file paths to base64 data URIs before passing the message to the aionrs engine.

Depends on

This change requires aionrs to support image content blocks first:

• feat: add image content block support for Aion CLI aionrs#196

Once that PR is merged and a new aionrs tag is released, this PR should be updated to point Cargo.toml to the new aionrs version.

How it works

When a user attaches an image to an Aion CLI conversation:

1. AionUi sends content like: user text\n\n[[AION_FILES]]\n/path/to/image.png plus a files array
2. enrich_content_with_files() reads the image, base64-encodes it, and replaces the path with data:image/png;base64,...
3. The aionrs engine parses the marker and creates proper text + image content blocks
4. The provider serializes those blocks into the correct OpenAI/Anthropic multimodal format

Files changed

• crates/aionui-ai-agent/src/manager/aionrs/agent.rs
  • Added enrich_content_with_files() to inline image file paths as data URIs
• crates/aionui-ai-agent/src/manager/aionrs/history_sanitize.rs
  • Handle ContentBlock::Image in history sanitization

Testing

• Built locally with modified aionrs
• Verified Aion CLI can now receive and process attached images