[FEATURE] Let me mark an agent session as completed / dismiss it from the agents view

What I'm running into

When I have several background agents going, some of them end up stuck on "Ready for review" or "Needs input" that I'm simply done with. I don't want to answer them or review them anymore — I no longer need that session.

Right now there's no way to just mark one as completed or dismiss it. So they pile up in the agents view and I can't tell the sessions I still care about apart from the ones I've already abandoned. The list keeps growing with things I'll never come back to.

What would fix it

A simple action to mark an agent session as done / dismiss it from the view — without having to respond to it or interact with it further. Ideally:

• A "mark as completed" or "dismiss" action on a session
• Dismissed sessions drop out of the active list (archived, not necessarily deleted)
• Bonus: being able to dismiss several at once

Why it matters

The agents view is only useful if it reflects what I actually still need to deal with. A way to clear out abandoned sessions would keep it readable and let me focus on the agents that genuinely need my attention.