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-lock.json

@@ -32,6 +32,7 @@
         "@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",
@@ -15101,6 +15102,44 @@
         "proxy-from-env": "^1.1.0"
       }
     },
+    "node_modules/axios-mock-adapter": {
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+      "resolved": "https://registry.npmjs.org/axios-mock-adapter/-/axios-mock-adapter-2.1.0.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "fast-deep-equal": "^3.1.3",
+        "is-buffer": "^2.0.5"
+      },
+      "peerDependencies": {
+        "axios": ">= 0.17.0"
+      }
+    },
+    "node_modules/axios-mock-adapter/node_modules/is-buffer": {
+      "version": "2.0.5",
+      "resolved": "https://registry.npmjs.org/is-buffer/-/is-buffer-2.0.5.tgz",
+      "integrity": "sha512-i2R6zNFDwgEHJyQUtJEk0XFi1i0dPFn/oqjK3/vPCcDeJvW5NQ83V8QbicfF1SupOaB0h8ntgBC2YiE7dfyctQ==",
+      "dev": true,
+      "funding": [
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/feross"
+        },
+        {
+          "type": "patreon",
+          "url": "https://www.patreon.com/feross"
+        },
+        {
+          "type": "consulting",
+          "url": "https://feross.org/support"
+        }
+      ],
+      "license": "MIT",
+      "engines": {
+        "node": ">=4"
+      }
+    },
     "node_modules/axios-retry": {
       "version": "4.5.0",
       "resolved": "https://registry.npmjs.org/axios-retry/-/axios-retry-4.5.0.tgz",