Make the workspace right pane a first-class tab host (#3287)

* feat(app): add persistent workspace side panes

Keep the common review and file-browsing workflow beside the active agent without tearing down pane contents. Workspace tabs now share one compact chip language, assistant file links route into the retained right pane, and diff/file trees share stable geometry.

* fix(app): localize pull request empty state

* test(app): update explorer pane coverage

* fix(app): preserve explorer pane workflows

* test(app): make explorer tab selection idempotent

* fix(app): persist workspace review pins

* fix(app): preserve sidebar scrim drag hook

* fix(app): restore companion pane interactions

* test(app): follow selected sidebar surface

packages/app/e2e/browser/workspace-agent-title-handoff.spec.ts

@@ -3,7 +3,10 @@ import { expectComposerVisible, submitMessage } from "../support/helpers/compose
 import { delayCreatedAgentInitialTailResponse } from "../support/helpers/agent-timeline-gate";
 import { delayBrowserAgentCreatedStatus } from "../support/helpers/new-workspace";
 import { seedWorkspace, type SeedDaemonClient } from "../support/helpers/seed-client";
-import { waitForWorkspaceTabsVisible } from "../support/helpers/workspace-tabs";
+import {
+  createAgentTabFromMenu,
+  waitForWorkspaceTabsVisible,
+} from "../support/helpers/workspace-tabs";
 import { getServerId } from "../support/helpers/server-id";
 import { buildHostWorkspaceRoute } from "@/utils/host-routes";
 
@@ -56,7 +59,7 @@ test.describe("Workspace agent title handoff", () => {
     try {
       await page.goto(buildHostWorkspaceRoute(getServerId(), workspace.workspaceId));
       await waitForWorkspaceTabsVisible(page);
-      await page.getByTestId("workspace-new-agent-tab-inline").click();
+      await createAgentTabFromMenu(page);
       await expectComposerVisible(page);
 
       const prompt = "Keep the optimistic agent pane visible during handoff";
@@ -99,7 +102,7 @@ test.describe("Workspace agent title handoff", () => {
     try {
       await page.goto(buildHostWorkspaceRoute(getServerId(), workspace.workspaceId));
       await waitForWorkspaceTabsVisible(page);
-      await page.getByTestId("workspace-new-agent-tab-inline").click();
+      await createAgentTabFromMenu(page);
       await expectComposerVisible(page);
 
       const promptTitle = "Investigate optimistic tab title handoff";