- Add height change detection (analogous to existing width detection)
- Auto-detect when content shrinks below maxLinesRendered and trigger
full re-render to clear leftover empty rows
- Only triggers when no overlays are active (overlays need padding)
Fixes empty rows appearing below footer when:
- Closing /tree or other selectors
- Clearing multi-line editor content
- Any component shrinking
Also adds regression tests for resize handling and content shrinkage.
