feat: Sprint 1 — Playwright e2e + sandbox orchestration (TDD)

- e2e: Playwright chat-flow (sign up -> chat) with api/web webServer harness
- api: sandbox services subset/media-proxy/manifest/gc + DockerClient contract
- api: SandboxManager orchestrator (fake-Docker tested); /health route
- 53 unit tests green; Playwright e2e green

e2e/tests/chat-flow.test.ts

@@ -0,0 +1,12 @@
+import { test, expect } from '@playwright/test';
+
+test('user signs up and sees the chat interface', async ({ page }) => {
+  await page.goto('/');
+
+  await page.getByLabel('Email').fill(`e2e-${Date.now()}@example.com`);
+  await page.getByLabel('Password').fill('password123');
+  await page.getByRole('button', { name: 'Sign up' }).click();
+
+  await expect(page.locator('.wursor-chat-input')).toBeVisible();
+  await expect(page.locator('.wursor-welcome')).toContainText('Describe what you want');
+});