dashboard: add close_on_jump to keep the dashboard open after a jump

[alebiscotto]

Why

Enter and the 1-9 quick jumps switch to the agent's pane and close the dashboard. When the dashboard is used as a monitor — hopping between a few agents to see what each is doing — that means reopening it after every hop.

p already switches without closing, but it is a separate key rather than a choice about how jumping behaves, so the muscle memory for Enter and the number keys is the one that keeps closing the view.

What

New dashboard.close_on_jump option, default true (today's behaviour):

dashboard:
  close_on_jump: false

The check sits next to the existing should_exit_on_jump() one in switch_to_pane_and_track, which means:

• every jump path is covered at once — Enter, the number keys and the Bksp toggle — instead of special-casing one binding;
• the jump itself is untouched, including the pane history that Bksp walks through, so this is purely about whether the view closes;
• multiplexers that already keep the dashboard open on a jump keep deciding for themselves.

p is unchanged and never closes the dashboard, whatever the setting.

Testing

• Two unit tests: the default stays true, and the option parses and disables closing.
• Full suite green (1419 passed), cargo fmt --check clean.