feat(run): add TerminalView xterm.js component for the PTY transport

- TerminalView.tsx: xterm.js component with WebSocket attachment to /ws-pty/:runId
- Test: validates WS connection URL, incoming terminal data, and outgoing keystrokes
- Added ResizeObserver stub to test-setup.ts for jsdom environment

client/src/test-setup.ts

@@ -16,6 +16,13 @@ import { afterEach, beforeEach } from "vitest";
 import "./i18n/index";
 import i18n from "i18next";
 
+/** jsdom does not implement ResizeObserver — stub it for components that use it. */
+// @ts-expect-error global stub
+global.ResizeObserver = class {
+  observe() {}
+  disconnect() {}
+};
+
 /** Pin locale to English — LanguageDetector may otherwise pick up zh/vi from the host OS. */
 beforeEach(() => {
   i18n.changeLanguage("en");