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.test.ts

@@ -45,14 +45,14 @@ describe("resolveNotificationTarget", () => {
 });
 
 describe("buildNotificationRoute", () => {
-  it("routes to workspace with one-shot open intent when workspace id is present", () => {
+  it("routes to the agent path when workspace id is present", () => {
     expect(
       buildNotificationRoute({
         serverId: "srv-1",
         agentId: "agent-1",
         workspaceId: "ws-main",
       }),
-    ).toBe("/h/srv-1/workspace/ws-main?open=agent%3Aagent-1");
+    ).toBe("/h/srv-1/agent/agent-1");
   });
 
   it("routes directly to server-scoped agent path when both ids are present", () => {