Improves form-filler instructions

[markwaddle]

Improves form-filler instructions:

• improves ability to identity and resolve conflicts
• improves ability to handle multiple files

Extends form-field model:

• to recognize "sections" in forms, for more context in extracted data, and improved populated-form rendering
• renders description and instructions in the populated-form

Additionally:

• further moves away from "agent" name to "extension", by moving out of the agents directory
• adds support for PNG files (screenshots, etc.)
• adds timestamps to user messages for current-date awareness
• fixes links in the app for already-copied conversations