The human-readable matrix MCP reference was missing three behaviours
documented only in the MCP server instructions string:
- send_file / download_file tools (issues 1829, 1830)
- [file:]/[image:]/[audio:]/[video:] attachment markers in read_room (issue 1830)
- unread guard: send_message, send_dm, send_file, send_reply all
reject if the room has unread messages (issue 1828)
- send_redact (omitted from the tool list entirely)
Add all four to docs/tools/matrix.md to match the MCP server
instructions added in the previous commit.