Preview panel state should persist when switching between sessions

Problem

When working with multiple sessions in Claude Code Desktop and using the preview feature, switching between sessions resets the preview panel entirely — it closes, and you have to reopen it and re-resize it every time you switch back.

This is particularly painful for workflows where the preview loop is central (e.g., prototyping UI with frequent visual verification). The friction of reopening + resizing the preview on every session switch adds up fast.

Expected Behavior

When switching between sessions in Claude Code Desktop, the preview panel should remember:

• Whether it was open or closed
• Its size/dimensions
• Its position (if applicable)

Each session should restore its own preview state when you switch back to it.

Current Behavior

Switching sessions resets preview panel state completely. The panel closes and must be manually reopened and resized.

Context

This matters most for multi-session workflows — e.g., using worktree-isolated sessions for parallel design explorations on the same project, where you're frequently switching between sessions to compare approaches. The preview is the primary feedback mechanism for visual work, so losing its state on every switch creates significant friction.