fix(session_picker): switch to remaining session when deleting active one

[hermandavid]

Summary

Fix <C-d> in the session picker creating a new session when deleting the active one instead of switching to a remaining session.

Problem

Deleting the active session always spawned a new session, even when other sessions existed. The user would land on an unexpected blank session, and the picker would show the leftover entries plus the freshly-created one. This was also inconsistent with deleting a non-active session, which simply removes the entry.

Fix

The delete action now switches to the most recently updated remaining session via core.switch_session, and only falls back to core.create_new_session when no sessions remain.

Behavior

• Active session deleted with others remaining → switch to most recent remaining.
• Active session deleted when it's the only one → create new (unchanged).
• Non-active session deleted → unchanged.

[sudo-tee]

Thanks this seems like a greast fix.