`/update` has limited feedback and can later interrupt session

### Describe the bug

On version 1.0.10, I used the `/update` command to check for updates. Nothing appear to happen. After waiting for 30 seconds or so, I started work, detailing out a prompt in plan mode. Then suddenly copilot quit out to update. After updating, it restarted but offered no explanation that it had even updated itself (it had, the version was now 1.0.12).

I would suggest

`/version` - provide immediate feedback - including progress if an update is being downloaded

After an update is downloaded, do not auto apply and quit, if it means user's work (mid prompt) is lost.

After a reboot, post update, post the release notes to the output, or at least tell the user an update has been applied and explain how to view the release notes.

Thanks!

### Affected version

_No response_

### Steps to reproduce the behavior

1. `/update`
2. Start work on a prompt
3. Lose session when copilot suddenly restarts

### Expected behavior

1. `/update`
2. Either - synchronous blocking progress than reboots at the end, or async update that prompts the user to restart when it's ready
3. Post update, message about the update having been applied and direct user to release notes

### Additional context

_No response_

Start by tracing the `/update` command flow and its interaction with `/version`, focusing on feedback, download timing, restart behavior, and release-note messaging. Verify that update progress or status is visible, active work is not unexpectedly lost, and the post-update output explains what happened and how to view release notes.

Written by the indexing model from the issue text.