Add app name column to `sandbox-pool list`

m sandbox-pool list shows a VERSION column that now renders a short ID, so there's no way to tell which app a pool belongs to. This is the same regression we fixed for sandbox list in MIR-1007 — the app name used to be legible in the version prefix, and short IDs hid it.

Add an explicit APP column to the table output (JSON output is unaffected since it serializes the full pool). The version→app lookup machinery is already present in the command since it walks app_version entities to compute the MODE column, so this should be a small change.