Add setting to hide/collapse file diff output in chat

Feature Request

Add a configurable setting to hide or collapse file diff output displayed in the chat after Edit/Write tool calls.

Current Behavior

Every file edit shows a full colored diff (red/green lines with line numbers) inline in the chat. For users who make many edits per session, this creates significant visual clutter and pushes the conversation history off-screen.

Desired Behavior

A setting in ~/.claude/settings.json such as:

{
  "showDiffs": false
}

Or a collapsible option that shows a summary line (e.g., "Updated index.html: +6 lines, -1 line") with the ability to expand to see the full diff if needed.

Why This Matters

• Visual noise — diffs dominate the chat view, making it hard to follow the conversation
• Scrolling fatigue — large edits push important context out of view
• Trust model — users on bypassPermissions mode have already opted into trusting edits; they can review via git diff when needed
• Consistency — Read tool output already shows a compact summary ("Read 25 lines"); Edit/Write could follow the same pattern

Suggested Options

1. "showDiffs": false — hide diffs entirely, show summary only
2. "showDiffs": "collapsed" — show summary with expandable detail
3. "showDiffs": true — current behavior (default)