(file-panel): the panel shell switches from bottom to top between Changes and Touched #503

What happens

The file panel puts its shell on a different side depending on the tab (v0.0.90 candidate, PR #500):

• Changes: the Changes editor on top, the panel shell below it.
• Touched: the panel shell on top, the Touched list below it.

Switching tabs moves the shell from bottom to top, so the prompt jumps across the panel. The maintainer confirms this is not intended.

Wanted

One layout for every tab of the panel, the shell always on the same side (and the splitter position shared or remembered per tab, to decide), with a jsdom or e2e test that switches Changes → Touched → Changes and asserts the shell keeps its position. See .ai/contexts/panel-terminal.md (mount point, splitter) and .ai/contexts/touched-files.md (#467/#468 put the Touched list on top and the editor below).