feat(app/e2e): introduce withWorkspace fixture and DSL helpers (#717)

Adds a `withWorkspace` Playwright fixture plus composable helpers
(permissions, sidebar, composer, agent-stream, settings) so specs read
as user-level intent. Migrates workspace-lifecycle and settings-host-page
to the new DSL as proof.

packages/app/e2e/helpers/sidebar.ts

@@ -0,0 +1,21 @@
+import { expect, type Page } from "@playwright/test";
+
+function requireServerId(): string {
+  const serverId = process.env.E2E_SERVER_ID;
+  if (!serverId) {
+    throw new Error("E2E_SERVER_ID is not set (expected from Playwright globalSetup).");
+  }
+  return serverId;
+}
+
+export async function selectWorkspaceInSidebar(page: Page, workspaceId: string): Promise<void> {
+  const row = page.getByTestId(`sidebar-workspace-row-${requireServerId()}:${workspaceId}`);
+  await expect(row).toBeVisible({ timeout: 30_000 });
+  await row.click();
+}
+
+export async function expectWorkspaceListed(page: Page, name: string): Promise<void> {
+  await expect(
+    page.locator('[data-testid^="sidebar-workspace-row-"]').filter({ hasText: name }).first(),
+  ).toBeVisible({ timeout: 30_000 });
+}