improve preface to prompt

[deansher]

Issue

Instead of, for example, Brade v0.60.7.dev99+gfe41e793.

Version and model info

No response

[deansher]

Add cwd and timestamp in preface to prompt (along with the file list)

Also, use separate sections for read-only vs editable files and drop the " (read only)", because it breaks copy/paste.