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/file-explorer-context-actions.spec.ts

@@ -3,6 +3,7 @@ import path from "node:path";
 import { expect, type Page } from "@playwright/test";
 import { test } from "../support/fixtures";
 import { openFileExplorer } from "../support/helpers/file-explorer";
+import { openChangesPanel } from "../support/helpers/workspace-tabs";
 import { gotoWorkspace } from "../support/helpers/launcher";
 import { daemonWsRoutePattern } from "../support/helpers/daemon-port";
 import { seedWorkspace, type SeededWorkspace } from "../support/helpers/seed-client";
@@ -437,7 +438,7 @@ test("hides unsupported file operations and revert actions", async ({ page }) =>
   await expect(filesMenu.getByText("Delete", { exact: true })).toHaveCount(0);
   await page.keyboard.press("Escape");
 
-  await page.getByTestId("explorer-tab-changes").click();
+  await openChangesPanel(page);
   await expect(page.getByTestId("diff-file-0")).toBeVisible({ timeout: 30_000 });
   await page.getByTestId("diff-file-0-toggle").click({ button: "right" });
   await expect(page.getByTestId("diff-file-0-duplicate")).toHaveCount(0);