Adds confirmation dialogs before archiving an agent or archiving an
agent and deleting its workspace. Previously, clicking these actions
in the TopBar or sidebar dropdown menus would immediately trigger
the destructive action with no confirmation step.

Both the AgentDetailTopBar and AgentsSidebar ChatTreeNode components
now show a ConfirmDialog (type 'delete') before proceeding. Storybook
stories cover dialog visibility and handler invocation for both
locations.

The confirmation dialog is only needed for the destructive
"Archive & Delete Workspace" flow, not the simple archive.
Reverts the archive menu items in both TopBar and AgentsSidebar
to call the handler directly, and removes the corresponding
storybook stories.

…alog

Displays the workspace name in 'owner/name' format in the
confirmation dialog for the 'Archive & Delete Workspace' action,
matching the pattern used elsewhere in the agents UI.

- TopBar: receives workspaceName as a prop from AgentDetail, which
  already fetches the workspace object.
- AgentsSidebar: fetches the workspace via useQuery(workspaceById)
  in ChatTreeNode to resolve the name from workspace_id.