Faster CLI startup, offline-friendly

The CLI no longer waits on the network at startup when you are already logged in, so commands stay fast offline and on flaky connections.

• Throttled the background update check so a burst of commands makes one network call per window instead of one per command.
• Made whoami cache-first, showing your identity instantly and refreshing only once a day.
• Slowed the station update-check cadence to favour stability on production benches.