MCP search and list tools now show which files are attached to each thought and insight.

When an AI agent searches or lists your thoughts and insights, each result now includes the list of files attached to it — asset id, title, description, MIME type, and kind (image, document, audio, etc.). This closes the loop that was opened in ticket 6: an agent that finds a thought can now immediately see its attachments and act on them (call get_asset for a signed download URL, or detach_asset to remove one) without a separate lookup step. This unblocks the real-world case where a user uploaded an image and asked their AI assistant to find it.