test: complete Phase 3 - comprehensive unit test coverage

- Implemented 943 unit tests across all services, parsers, and infrastructure
- Created shared test utilities (test-helpers, assertions, data-generators)
- Achieved high coverage for critical services:
  - n8n-api-client: 83.87%
  - workflow-diff-engine: 90.06%
  - node-specific-validators: 98.7%
  - enhanced-config-validator: 94.55%
  - workflow-validator: 97.59%
- Added comprehensive tests for MCP tools and documentation
- All tests passing in CI/CD pipeline
- Integration tests deferred to separate PR due to complexity

Total: 943 tests passing, ~30% overall coverage (up from 2.45%)

package.json

@@ -98,6 +98,7 @@
     "@types/ws": "^8.18.1",
     "@vitest/coverage-v8": "^3.2.4",
     "@vitest/ui": "^3.2.4",
+    "axios-mock-adapter": "^2.1.0",
     "fishery": "^2.3.1",
     "msw": "^2.10.4",
     "nodemon": "^3.1.10",