Add comprehensive E2E test framework with Playwright

[Copilot]

This PR implements a complete end-to-end testing framework using Playwright to cover both API endpoints and UI functionality as requested in the issue.

🧪 Test Framework Setup

• Playwright Configuration: Cross-browser testing (Chromium, Firefox, WebKit) with auto-start dev servers
• Test Structure: Organized in /test/e2e/ with comprehensive coverage
• npm Integration: npm test command runs all tests from repository root
• Developer Experience: Added npm run test:headed and npm run test:ui for interactive testing

📋 Test Coverage

API Endpoint Tests (test/e2e/api-*.spec.ts)

• Document Upload (documents-post.ts): PDF file upload validation, multipart form handling, error cases
• Document Retrieval (documents-get.ts): File download, 404 handling, content-type validation
• Chat Streaming (chats-post.ts): NDJSON streaming responses, session management, error handling

UI Tests (test/e2e/ui-chat.spec.ts)

• Chat interface display and component validation
• Message sending/receiving workflows
• Suggestion click handling
• User ID generation and localStorage persistence
• New chat functionality

Full E2E Workflows (test/e2e/full-workflow.spec.ts)

• Complete Integration: Document upload → Chat about uploaded content
• Multi-document Management: Parallel uploads and retrieval validation
• Session Continuity: Multiple questions with conversation history

🛠 Infrastructure

• Linting: Updated XO configuration with test-specific rules
• Documentation: Comprehensive README in /test/e2e/ with usage instructions
• Git Ignore: Test artifacts excluded from version control
• Dependencies: Added @playwright/test with proper TypeScript support

📊 Test Statistics

54 tests across 4 test files providing comprehensive coverage:

• 8 API endpoint tests
• 8 UI interaction tests
• 3 full workflow integration tests
• Cross-browser multiplication (3 browsers × 18 base tests)

🚀 Usage

# Install Playwright browsers (first time only)
npx playwright install

# Start dev servers
npm run start:api  # Terminal 1
npm run start:webapp  # Terminal 2

# Run tests
npm test

The framework validates both the 2 base scenarios mentioned in the issue:

1. ✅ File Upload: Tests document upload via /api/documents endpoint
2. ✅ Chat UI: Tests chat interface asking questions about indexed documents

Fixes #5.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• functionscdn.azureedge.net
  • Triggering command: node lib/install.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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