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/e2e/settings-navigation.spec.ts

@@ -45,7 +45,7 @@ test.describe("Settings sidebar navigation", () => {
     await expectGeneralContent(page);
   });
 
-  test("/h/[serverId]/settings redirects to /settings/hosts/[serverId]", async ({ page }) => {
+  test("/h/[serverId]/settings redirects to the host connections section", async ({ page }) => {
     await gotoAppShell(page);
     await verifyLegacyHostSettingsRedirect(page);
   });
@@ -132,7 +132,9 @@ test.describe("Settings — compact master-detail", () => {
     await expectSettingsBackButton(page);
   });
 
-  test("tapping a host entry pushes /settings/hosts/[serverId]", async ({ page }) => {
+  test("tapping a host section row pushes /settings/hosts/[serverId]/connections", async ({
+    page,
+  }) => {
     await gotoAppShell(page);
     await openCompactSettings(page);