fix: add missing validations/unit-tests.yaml example

Add the missing workflow validation example and keep the #1039 TDD regression active by removing the expected-fail tag and updating scenario narrative.\n\nTo satisfy the required full quality gates, stabilize flaky integration behavior encountered during this issue run: use a shared SQLAlchemy session in resource DAG scripts, isolate RxPY validation temp paths per test run, extend transient subprocess timeouts/retry behavior, and clear stale pabot worker artifacts before integration runs so repeated nox executions are reliable.\n\nISSUES CLOSED: #1039

examples/validations/unit-tests.yaml

@@ -0,0 +1,24 @@
+# Example: Required validation for unit tests
+# Mirrors the workflow example in docs/specification.md (Example 1, Step 1).
+
+name: local/unit-tests
+description: Unit tests
+source: custom
+mode: required
+code: |
+  import subprocess
+
+  def run(input_data):
+      result = subprocess.run(["pytest", "tests/"], capture_output=True, text=True)
+      passed = result.returncode == 0
+      return {
+          "passed": passed,
+          "message": "Unit tests passed" if passed else "Unit tests failed",
+          "data": {
+              "stdout": result.stdout,
+              "stderr": result.stderr,
+              "returncode": result.returncode,
+          },
+      }
+
+timeout: 300