Add comprehensive test suite with Vitest and Playwright

- Convert from Jest to Vitest with Playwright browser provider for real DOM testing
- Add extensive tests for all bug fixes (memory leaks, state mutations, logic errors)
- Add extract.spec.mjs with comprehensive field extraction tests
- Add group.spec.mjs with tests for beaker/group functionality
- Enhance dirty.spec.mjs, enrichment.spec.mjs, and event.spec.mjs with bug-specific tests
- Configure Vitest with Playwright for authentic browser environment testing
- Add test scripts for watch, UI, and coverage modes
- Tests validate all 15 bugs fixes with edge cases and integration scenarios

Co-authored-by: tanepiper <376930+tanepiper@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -107,6 +107,9 @@ dist
 .moon/cache
 .moon/docker
 
+# Vitest
+__screenshots__/
+
 # OSX
 
 .DS_Store