Improve the Files panel with relative paths, sorting, grouping, and diffs

[raphant]

Problem

The Files panel sorts only by token count and truncates paths with a generic prefix.
Absolute and encoded Claude project paths can be difficult to recognize.
The panel does not expose the latest edit or group files by repository or agent.

Proposed change

Display project-relative paths when the workspace is known.
Add sorting, grouping, and a latest-diff action without changing file tracking.

Acceptance criteria

• The panel prefers workspace-relative paths and keeps the full path in accessible detail text.
• Users can sort by recency, reads, edits, tokens, and agent count.
• Users can group files by repository or agent.
• VS Code users can open the file or its latest recorded diff.
• Standalone users get a copy-path action when direct file opening is unavailable.

Source

• web/components/agent-visualizer/file-attention-panel.tsx owns the current list and token sort.