Add markdown-to-HTML rendering for assistant messages using Markdig with
HTML sanitization. Includes cached rendering to avoid lag during streaming,
styled markdown elements (code blocks, tables, lists, blockquotes) within
chat bubbles, and 18 unit tests covering rendering and XSS prevention.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Create ChatAgent.Api.Tests and ChatAgent.Client.Tests projects with xUnit
and Moq. Test HealthController (200 + valid response), ChatController
(SSE streaming with mocked upstream, error handling), and ChatApiClient
(delta parsing, error events, health endpoint). 6 tests, all passing.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
