Support attachments (screenshots, CSV) in Metabot

**Describe the solution you'd like.**
It would be great if we added support for attachments in Metabot, including screenshot uploads and CSV files. This is so we can give Metabot references to help build reports.
The customer noted that this is a standard experience with other LLMs.

**How does this feature request impact you?**
Improve the Metabot experience

**Additional information**
Customer request

The issue names no files, tests, or entry points, so first locate Metabot's current message and attachment handling. Clarify the supported screenshot and CSV formats, upload behavior, and report-reference workflow before implementation; done means both attachment types work as Metabot references.

Written by the indexing model from the issue text.