Flatten settings sidebar with a host picker (#1241)

* Flatten settings sidebar with a host picker

Settings had two implicit tiers: app-level sections as flat sidebar rows,
and per-host settings hidden behind a drill-in to one monolithic host page.
This flattens both into a single sidebar with an "App" group and a "Host"
group, where the host's settings are top-level rows scoped by a host picker.

- Split the monolithic HostPage into four section pages: Connections,
  Orchestration (was the unnamed inject-tools + system-prompt block),
  Providers, and Daemon (status, updates, restart, remove).
- Host picker reuses the canonical <Combobox> sidebar host switcher; defaults
  to the local host so a single-local-host user never thinks about "the daemon".
- Host sections become real sub-routes (/settings/hosts/[id]/[section]); the
  old /settings/hosts/[id] redirects to the connections section, so existing
  deep links (pairing, workspace, open-project) keep working.
- "Open providers" from the project screen now lands on the Providers section.

* Fix e2e host-settings navigation for the flat sidebar

The flat-settings refactor moved host settings onto separate section pages,
but three e2e helpers still expected the old monolithic host page:

- openDesktopSettings: the daemon-lifecycle card now lives on the Daemon
  section — navigate there before asserting it.
- acp catalog: "Add provider" now lives on the Providers section — open that
  section before opening the add-provider modal.
- openAddHostFlow: "Add host" is now an item inside the host picker (Combobox),
  not a standalone button — open the picker first.

Test-only; no product changes. Fixes the 8 playwright failures on this branch.

packages/app/src/screens/open-project-screen.tsx

@@ -17,7 +17,7 @@ import {
 import { TitlebarDragRegion } from "@/components/desktop/titlebar-drag-region";
 import { useIsLocalDaemon } from "@/hooks/use-is-local-daemon";
 import { PairDeviceModal } from "@/desktop/components/pair-device-modal";
-import { buildHostAgentDetailRoute, buildSettingsHostRoute } from "@/utils/host-routes";
+import { buildHostAgentDetailRoute, buildSettingsHostSectionRoute } from "@/utils/host-routes";
 import { ImportSessionSheet } from "@/components/import-session-sheet";
 import { useHostRuntimeClient } from "@/runtime/host-runtime";
 import { useOpenProject } from "@/hooks/use-open-project";
@@ -62,7 +62,7 @@ export function OpenProjectScreen({ serverId }: { serverId: string }) {
   );
 
   const handleOpenProviders = useCallback(() => {
-    router.push(buildSettingsHostRoute(serverId));
+    router.push(buildSettingsHostSectionRoute(serverId, "providers"));
   }, [router, serverId]);
 
   return (