feat: Add Playwright testing scaffolding infrastructure

Implements complete Playwright testing infrastructure for manual MCP testing and
as foundation for Magnitude tests.

Created:
- playwright.config.ts - Main configuration with setup project
- tests/playwright/auth.setup.ts - Authentication setup (placeholder)
- tests/playwright/fixtures.ts - Custom fixtures for authenticated/page contexts
- tests/playwright/helpers/chat.ts - Chat interaction helpers
- tests/playwright/helpers/galaxy.ts - Galaxy visualization helpers
- tests/playwright/helpers/node.ts - Node creation/management helpers
- tests/playwright/smoke.spec.ts - Basic smoke tests
- .env.test - Environment variables template

Updated:
- package.json - Added test:playwright scripts
- .gitignore - Added tests/playwright/.auth/ exclusion

Ready for manual Playwright MCP testing and Magnitude test creation.

Resolves plan: 01-playwright-scaffolding.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/playwright/auth.setup.ts

@@ -0,0 +1,12 @@
+import { test as setup, expect } from '@playwright/test';
+
+const authFile = 'tests/playwright/.auth/user.json';
+
+setup('authenticate', async ({ page }) => {
+  // For now, just create an empty auth file
+  // TODO: Implement actual OAuth flow when test credentials are available
+  console.log('[Auth Setup] Skipping authentication - implement OAuth flow with test credentials');
+
+  // Save empty state for now
+  await page.context().storageState({ path: authFile });
+});