[Feature] File activity heatmap — which files Claude touched most

[anaypaul]

What

Add a "Files" tab with a treemap showing which files were read/written/edited most during the session. Size = frequency, color = operation type (blue=read, green=write, red=error).

Why

After a long session, developers ask "what files did Claude actually touch?" — this answers it at a glance.

How

• New src/components/FileActivityMap.tsx component
• Parse toolCall.input.file_path from Read/Write/Edit tool calls
• Use Recharts Treemap (already a dependency)
• Click a file to filter the timeline to tool calls involving that file
• No backend changes needed

Complexity

Medium — 8-12 hours.