test: add comprehensive test suite for api-helper.ts

- Add 32 tests covering all functions in api-helper.ts
- Test errToStr() with Error instances, API errors, ErrorEvent, strings, and edge cases
- Test extractAgents() and extractAllAgents() with various workspace configurations
- Validate Zod schemas for AgentMetadataEvent
- Update CLAUDE.md to reflect standard test running approach
- All 137 tests now passing

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jaggederest

CLAUDE.md

@@ -7,8 +7,7 @@
 - Package: `yarn package`
 - Lint: `yarn lint`
 - Lint with auto-fix: `yarn lint:fix`
-- Run all tests: `yarn test:ci` (always use CI mode for reliable results)
-- Run specific test: `yarn test:ci ./src/filename.test.ts`
+- Run all tests: `yarn test:ci` (always use CI mode for reliable results, runs all test files automatically)
 - Watch mode (development only): `yarn test`
 - Run tests with coverage: `yarn test:coverage`
 - View coverage in browser: `yarn test:coverage:ui`