Ability to pause all agents

### Feature summary

A option to pause all agents at the next logical turn so that the system can sleep or restart easily

### What problem are you trying to solve?

At the end of the work day I need to take my laptop home with me but if an agent is running I'm stuck until it stops, or I need to stop it then prompt with `continue` the next day across everything. Similarly when there's an app update it stops all agents and they need to be manually restarted.

### Proposed solution

An option that allows pausing all running agents at the next turn along with an option to then resume all agents.

This could also be tied into the update mechanism where agents are paused and then automatically resumed when the update starts

### Workflow impact

This would affect all users that aren't able to leave their machines running 24/7 - it would allow us to worry less about managing agent lifecycles and sitting there hoping the copilot would finish already so we can go home for the day

### Installation context

_No response_

### Additional context

I would expect that there would need to be some sort of overlay that shows the status of each agent so you can see what haven't reached a turn / pause point yet - and equally we would need a way to know that agents were paused and how to resume them.

An open question would be whether the whole app is paused, or if it's per agent but with a global control — i.e. if you paused all agents can you start a new one and leave the others paused?

The issue names no files, tests, or entry points, so start by locating the agent lifecycle and update-handling surfaces in the desktop app. Done should include a global pause-at-next-turn control, visible per-agent pause status, and a way to resume agents while resolving whether new agents remain runnable.

Written by the indexing model from the issue text.