Show host in search results and filter sidebar by multiple hosts (#1825)

* feat(app): show host in command center and multi-select host filter

Command-center agent results now show which host the workspace lives on,
shown only when more than one host is connected (matching the sidebar).

The sidebar display-preferences filter becomes multi-select — pick any
number of hosts instead of one-or-all — and its host rows now carry a
status dot on the left like the other host pickers. Persisted filter
state migrates from the old single host to a host list.

* test(app): extract host-filter and command-center e2e DSL helpers

Move the mechanical menu/search interactions out of the new spec bodies
into focused helpers so the tests read as user intent.

* fix(app): drop the icon from the host filter "All hosts" item

* fix(app): make multi-host e2e seeding order-independent

The offline-host seed relied on Playwright running the test's init script
after the fixture's registry reset — an ordering Playwright does not
guarantee. Write the full registry and set the fixture's disable-once flag,
then reload, so the multi-host seed survives regardless of script order.

Also tag the pre-v2 hostFilter migration reader with COMPAT so the cleanup
sweep can find it.

packages/app/src/components/sidebar-workspace-list.test.tsx

@@ -256,7 +256,7 @@ function WorkspaceSelectionProbe({
 
 function SidebarFrameProbe({ counts }: { counts: RenderCounts }): ReactElement {
   counts.frame += 1;
-  const { projects } = useSidebarWorkspacesList({ hostFilter: SERVER_ID });
+  const { projects } = useSidebarWorkspacesList({ hostFilters: [SERVER_ID] });
 
   return (
     <>