Integrate Stagehand for Browser Automation in TestAgent

- Updated TestAgent to incorporate Stagehand for browser automation, enabling AI-driven interactions with web pages.
- Implemented browser session management, including persistence across phases and error handling.
- Enhanced logging capabilities by capturing console logs and network errors during browser sessions.
- Added TypeScript types for browser session, console logs, and network errors to improve type safety.
- Created integration tests to validate browser binding access, browser launch, and session persistence.

This commit addresses Story 2.2: Browser Rendering integration with Stagehand.

Author: adam0white

docs/sprint-status.yaml

@@ -46,7 +46,7 @@ development_status:
 
   epic-2: contexted
   2-1-testagent-durable-object-skeleton: done
-  2-2-browser-rendering-integration-and-stagehand-setup: ready-for-dev
+  2-2-browser-rendering-integration-and-stagehand-setup: done
   2-3-phase-1-load-validation: ready-for-dev
   2-4-phase-2-control-discovery: ready-for-dev
   2-5-phase-3-gameplay-exploration-with-computer-use: ready-for-dev