Merge sidebar workspaces across all connected hosts (#1538)

* Merge workspaces across all hosts in the sidebar

Replace per-host sidebar sections with a single merged project list.
Projects that exist on multiple hosts (matched by projectKey) are
collapsed into one row. Host identity is surfaced via:

- A status-only footer pill showing online/offline host counts
- Hover cards with a mandatory host row on every workspace entry
- Subtitles showing the host name when a project spans >1 host
- A host filter in the grouping dropdown (not a sidebar switcher)

Order and group-mode stores migrated from per-server to global keys
with zustand persist migrations. New-workspace screen now shows a
merged project list with a host selector combobox.

Key files:
- workspace-structure.ts: merge algorithm by projectKey
- sidebar-view-store.ts / sidebar-order-store.ts: global state
- sidebar-workspace-list.tsx: context-based subtitle injection
- new-workspace-screen.tsx: host selector in footer row

* Add host filtering to the merged sidebar

The sidebar now merges workspaces from every connected host, so a single
global "active host" no longer fits. Host selection becomes explicit per
action via a host chooser, and agent history pages across all hosts at
once. Removes the active-host / active-server-id model and the
all-agents-list hook that fed it.

* Fix rebase fallout: translate archive host error, update stale workspace-key test

archiveWorkspacesOptimistically used a raw "Host is not connected" string
that the i18n completeness test forbids; route it through i18n.t with the
existing hostDisconnected key. The selectors memoization test asserted
un-prefixed workspace keys, but merged-sidebar keys are serverId-prefixed.

* Fix sidebar review fallout

* Address sidebar review followups

* Fix sidebar workspace identity migration

* Address sidebar review followups

* Handle partial host history failures

* Fix merged sidebar project removal and E2E drift

* Restore history routes and project removal shape

* Remove sidebar host context plumbing

* Tighten sidebar status and host filter state

* Keep new workspace project selection host-compatible

* Migrate sidebar view storage

* Streamline host selection flows

* Update all-host history on archive

* Fix empty project sidebar action

Code regression: the main merge dropped the empty-project New workspace child row while keeping the empty project persistence contract. Restore the row using the project host target so the sidebar stays aligned with the no-host-selection model.

* Fix Japanese shortcut translation key

Stale-base integration: main added the Japanese locale after this branch added cycleAgentMode to the English shortcut help map. Merging main exposed the missing ja key in CI typecheck and resources.test.

* Fix Playwright speech teardown race

packages/app/src/utils/sidebar-shortcuts.test.ts

@@ -24,6 +24,7 @@ function workspace(input: {
     serverId: input.serverId,
     workspaceId: input.workspaceId,
     projectKey: input.projectKey ?? "project-default",
+    projectName: input.projectKey ?? "Project",
     workspaceDirectory: input.workspaceDirectory,
     projectKind: "git",
     workspaceKind: "checkout",
@@ -48,7 +49,13 @@ function project(projectKey: string, workspaces: SidebarWorkspaceEntry[]): Sideb
     projectName: projectKey,
     projectKind: "git",
     iconWorkingDir: workspaces[0]?.workspaceDirectory ?? "",
-    canCreateWorktree: true,
+    hosts: [
+      {
+        serverId: workspaces[0]?.serverId ?? "s1",
+        iconWorkingDir: workspaces[0]?.workspaceDirectory ?? "",
+        canCreateWorktree: true,
+      },
+    ],
     workspaces,
   };
 }
@@ -139,7 +146,10 @@ describe("buildSidebarShortcutModel", () => {
       }),
     ]);
     directoryProject.projectKind = "directory";
-    directoryProject.canCreateWorktree = false;
+    directoryProject.hosts = directoryProject.hosts.map((host) => ({
+      ...host,
+      canCreateWorktree: false,
+    }));
 
     const model = buildSidebarShortcutModel({
       projects: [gitProject, directoryProject],