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/agent-message-submission.spec.ts

@@ -24,7 +24,10 @@ import {
 } from "../support/helpers/composer";
 import { openAgentRoute, seedMockAgentWorkspace } from "../support/helpers/mock-agent";
 import { seedWorkspace } 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";
 import { WORKSPACE_DECK_MAX_MOUNTED_WORKSPACES } from "@/screens/workspace/workspace-deck-retention";
@@ -755,7 +758,7 @@ async function expectRenderedBefore(first: Locator, second: Locator): Promise<vo
 async function openWorkspaceDraft(page: Page, workspaceId: string): Promise<void> {
   await page.goto(buildHostWorkspaceRoute(getServerId(), workspaceId));
   await waitForWorkspaceTabsVisible(page);
-  await page.getByTestId("workspace-new-agent-tab-inline").click();
+  await createAgentTabFromMenu(page);
   await expectComposerVisible(page);
 }