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/helpers/desktop-updates.ts

@@ -2,7 +2,7 @@ import { readFileSync } from "node:fs";
 import { expect, type Page } from "@playwright/test";
 import { openSettings } from "./app";
 import { getE2EDaemonPort } from "./daemon-port";
-import { openSettingsHost } from "./settings";
+import { openSettingsHost, openSettingsHostSection } from "./settings";
 
 interface DaemonApiStatus {
   version: string;
@@ -208,6 +208,9 @@ export async function injectDesktopBridge(page: Page, config: DesktopBridgeConfi
 export async function openDesktopSettings(page: Page, serverId: string): Promise<void> {
   await openSettings(page);
   await openSettingsHost(page, serverId);
+  // The daemon-lifecycle card moved to the Daemon section in the flat-settings
+  // layout; navigate there before asserting it.
+  await openSettingsHostSection(page, serverId, "daemon");
   await expect(page.getByTestId("host-page-daemon-lifecycle-card")).toBeVisible({
     timeout: 15_000,
   });