Plan review UI: show plan title instead of generic 'Claude'\''s Plan'

Feature Request

When using plan mode, the plan review UI always shows "Claude's Plan" as the header, regardless of the actual plan content or filename.

Problem

When working with multiple plans simultaneously (reviewing 2-3 plans at once), there's no way to distinguish them in the review UI. The filename is a random string (e.g., ticklish-spinning-rabin.md) which doesn't help either.

Proposed Solution

Use the first H1 heading from the plan markdown file as the display title in the plan review UI. For example, if the plan file starts with:

# Plan: Redirect Chain Resolution bij Google Ads Import

The review UI should show "Redirect Chain Resolution bij Google Ads Import" instead of "Claude's Plan".

Fallback

If no H1 heading is found, fall back to the current "Claude's Plan" label.

Why

Users who work on multiple features in parallel often have several plans open for review. Being able to tell them apart at a glance is essential for an efficient workflow.