[Feature Request] Add diff view for PLAN.md changes to highlight modifications instead of reprinting entire plan

Feature Description
I LOVE PLAN.md mode.

Still, when working in plan mode there are several annoying things and fixing them would make it so much better.

Claude repeatedly prints the entire plan, even if we ask for a tiny tweak. Then I have to review the entire thing again, And again. And again.

This is INFORMATION OVERLOAD.

I get to the point I just give up and don't review it anymore and let it run, only to find out the plan had things I would have corrected.

It would be super helpful if after a user reviews a plan and then requests a change to show the human readable equivalent of a diff so we can see what Claude _just_ changed as opposed to having to re-read the entire plan to see the changes ourselves.

Just ask any lawyer who reviews changes to contract how impossible their jobs would be without redlining and black-lining. We need that for Claude.

Also, a user should be able to toggle between diff and full plan when they want. Maybe Claude could just display the entire document in dimmer color and the changes in brighter color, although that might not be accessible.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.32
• Feedback ID: 376ff368-d8a6-4027-ae91-63430da7b3e1