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/helpers/chat.ts

@@ -0,0 +1,35 @@
+import { Page, expect } from '@playwright/test';
+
+export class ChatHelper {
+  constructor(private page: Page) {}
+
+  async sendMessage(message: string) {
+    const input = this.page.locator('textarea[placeholder*="Type"], input[placeholder*="Type"]');
+    await input.fill(message);
+    await input.press('Enter');
+  }
+
+  async waitForAIResponse() {
+    // Wait for typing indicator to appear then disappear
+    const typingIndicator = this.page.locator('[data-testid="typing-indicator"]').first();
+    
+    try {
+      await typingIndicator.waitFor({ state: 'visible', timeout: 2000 });
+      await typingIndicator.waitFor({ state: 'hidden', timeout: 30000 });
+    } catch {
+      // Typing indicator might not appear for fast responses
+      await this.page.waitForTimeout(1000);
+    }
+  }
+
+  async getLastMessage() {
+    const messages = this.page.locator('[data-testid="chat-message"]');
+    const count = await messages.count();
+    return count > 0 ? messages.nth(count - 1) : null;
+  }
+
+  async getMessageCount() {
+    const messages = this.page.locator('[data-testid="chat-message"]');
+    return await messages.count();
+  }
+}