Add full test suite with unit, integration, and E2E smoke tests.

Introduce test.bat orchestrating Go/Vitest/Playwright phases, expand coverage across server, agent, and dashboard, and document in tests/README.md.

server/web/playwright.config.ts

@@ -0,0 +1,12 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './e2e',
+  timeout: 60_000,
+  retries: 0,
+  use: {
+    baseURL: process.env.AETHERFORGE_URL || 'http://127.0.0.1:8989',
+    trace: 'on-first-retry',
+  },
+  projects: [{ name: 'chromium', use: { ...devices['Desktop Chrome'] } }],
+});