desktop: refocus prompt input when switching tabs with Cmd+number

Description

Switching session tabs with Cmd+<number> should automatically focus the destination tab's prompt input. Currently, the tab changes without refocusing the input, interrupting keyboard-only navigation.

Steps to reproduce

1. Open at least two session tabs.
2. Switch between them using Cmd+1, Cmd+2, etc.
3. Start typing immediately after switching, including when returning to a previously visited tab.

Expected: The selected tab's prompt input receives focus, so typing works without an extra click.

Actual: The selected tab's prompt input is not automatically refocused.

Additional context

• Reported behavior; not independently reproduced. Exact app version and OS version were not provided.
• Related: #44244 reports similar focus loss on Windows. This report specifically covers Command-number tab switching; a shared cause has not been confirmed.

Requested by: @R44VC0RP (vogel via Slack)

Start by locating the Command-number session-tab switching handler and the destination tab's prompt input focus logic. Reproduce the behavior with multiple session tabs, including returning to a previously visited tab, and compare keyboard focus before and after switching. Done means typing works immediately after each Command-number switch without an extra click.