Show two worktrees side by side in one window (split view) #31015

Problem

When working in two worktrees at once (for example, an agent running in one while I review or test in another), I have to keep switching back and forth in the sidebar. Only one worktree is ever on screen, so I can't watch both terminals at the same time in one Orca window.

Proposal

Let a user open a second worktree beside the current one, in the same window:

• Right-click a worktree in the sidebar → Open in Split View puts it on the right half; the current worktree stays on the left.
• Both sides stay live (terminals keep rendering and are not parked). Clicking a side gives it keyboard input.
• A divider between the two halves can be dragged to resize, and has a close button. Close Split View is also in the context menu.
• Activating a worktree outside the pair ends the split.
• The split survives quitting and relaunching Orca (focus restored, width back to 50:50). If either side no longer exists, Orca quietly opens just the remaining worktree.
• Works for worktrees from two different repositories, and for SSH worktrees.

I have a working implementation and would be happy to open a PR for this.