Fix cold workspace URL sidebar navigation

Directly opening a workspace URL created a different React Navigation state shape than entering from /. Expo Router parsed the URL as a workspace layout route with a nested index child whose route.path and params pointed at the original workspace. Later sidebar navigation used router.dismissTo for another workspace. React Navigation's POP_TO reused the existing workspace route by name and updated the parent params, but preserved the nested child state. The result was a hybrid state: parent workspace params for B, child index path for A. Expo Router serialized the focused child path, so the address bar stayed on A and sidebar clicks looked like no-ops.

The fix is to stop using workspace/[workspaceId]/_layout.tsx as the actual screen. That layout did not render a Slot, so it only added an extra navigation level for Expo Router to preserve. Move the workspace UI, bootstrap boundary, open-intent consumption, and retained WorkspaceDeck into the leaf index route, making /h/:serverId/workspace/:workspaceId one real rendered route.

Keep workspace switches on navigateToWorkspace/router.dismissTo. This is not another replace workaround: replace previously created duplicate mounted workspace shells. The route-shape fix removes the stale nested child state that made dismissTo fail after cold deep links.

Also route archive/new-agent and notification flows through the centralized workspace navigation path so they do not bypass the same route contract.

Regression coverage: cold-load workspace A, click workspace B in the sidebar, and assert the URL changes to B. Verified with workspace-navigation-regression.spec.ts, settings-navigation.spec.ts, npm run typecheck, and npm run lint.

packages/app/src/utils/notification-routing.ts

@@ -1,9 +1,5 @@
 import type { Href } from "expo-router";
-import {
-  buildHostAgentDetailRoute,
-  buildHostRootRoute,
-  buildHostWorkspaceRoute,
-} from "@/utils/host-routes";
+import { buildHostAgentDetailRoute, buildHostRootRoute } from "@/utils/host-routes";
 
 type NotificationData = Record<string, unknown> | null | undefined;
 type NotificationRoute = Extract<Href, string>;
@@ -30,12 +26,8 @@ export function resolveNotificationTarget(data: NotificationData): {
 }
 
 export function buildNotificationRoute(data: NotificationData): NotificationRoute {
-  const { serverId, agentId, workspaceId } = resolveNotificationTarget(data);
+  const { serverId, agentId } = resolveNotificationTarget(data);
   if (serverId && agentId) {
-    if (workspaceId) {
-      const base = buildHostWorkspaceRoute(serverId, workspaceId);
-      return `${base}?open=${encodeURIComponent(`agent:${agentId}`)}` as const;
-    }
     return buildHostAgentDetailRoute(serverId, agentId);
   }
   if (serverId) {