Dismiss a workspace stuck on "Working", and make "Mark as read" actually clear a failed one

[thatdaveguy1]

What am I trying to do

Two things when I glance at the sidebar:

1. If an agent shows Working but isn't actually making progress (the provider wedged and never sent a terminal event), I want to manually dismiss it back to Done so the pulsing "working" dot goes away — without cancelling the agent's underlying turn.
2. When a workspace has failed, I want to acknowledge it once and have the red badge/group actually disappear, instead of the failure staying there forever.

How I do it today

1. For a stuck Working workspace: there is nothing. It sits in the Working group with the pulsing dot until I archive the workspace, reload the agent, or restart the daemon — even though the work is clearly finished or dead.
2. For a Failed workspace: right-click → Mark as read. The unread flag clears, but the workspace stays in the Failed group with its red dot, and the menu item remains clickable (and does nothing on repeat). I see this with both Pi and OMP agents.

Where Paseo gets in the way

• "Mark as read" is currently gated to attention and failed statuses — a running/Working workspace is never dismissible, so a stuck one is stuck.
• The acknowledge path is incomplete: it clears the unread flag but not the underlying failure state, so the red badge persists. The action looks like it works and doesn't.

What would the flow look like if it worked for me

1. A stuck Working workspace gets a "Mark as done" action (same context menu as "Mark as read"). Clicking it moves the workspace to Done and stops the pulse. It should not interrupt a genuinely-live agent — I only want to stop seeing the animation, and if the agent is actually still running, a late real result should be allowed to surface.
2. A Failed workspace's "Mark as read" (or "Acknowledge") actually moves it out of the Failed group, clearing the red badge, so the failure is dismissed until the agent fails again.

Both are closely related to #2687 (which is about passively detecting a stuck turn via a heartbeat) — that solves "can I tell it's stuck", this is about "give me a way to dismiss it once I know". The inverse direction (Done → "Ready to review") is already proposed in #2166 via a workspace.set_attention RPC, so a dismissal action would slot beside it.