ci(hipdnn-superbuild): add nightly CPU ref verification for bundle tests

Add a schedule trigger (daily 07:17 UTC) and workflow_dispatch to the
superbuild CI.  On nightly/manual runs the Linux job re-runs bundle
integration tests with HIPDNN_TEST_VERIFICATION_MODE=cpu, providing an
independent correctness check against the CPU reference executor
regardless of whether golden data is present.

PR CI is unaffected — the step is skipped on pull_request events.

JIRA: ALMIOPEN-2390

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bghimireamd

.github/workflows/hipdnn-superbuild-ci.yml

@@ -13,6 +13,9 @@ on:
       - '.github/workflows/hipdnn-superbuild-ci.yml'
       - 'projects/hipdnn/**'
       - 'dnn-providers/**'
+  schedule:
+    - cron: '17 7 * * *'
+  workflow_dispatch:
 permissions:
   contents: read
 
@@ -288,6 +291,12 @@ jobs:
       - name: Run tests
         run: ctest --test-dir build --output-on-failure
 
+      - name: Run CPU ref verification (nightly)
+        if: github.event_name == 'schedule' || github.event_name == 'workflow_dispatch'
+        env:
+          HIPDNN_TEST_VERIFICATION_MODE: cpu
+        run: ctest --test-dir build --output-on-failure -L external_integration_test
+
       - name: Patch ROCm SDK with superbuild outputs
         run: cmake --install build --prefix "$ROCM_SDK_PATH"