ci: run audit-orphans.sh on every PR + weekly cron

.github/workflows/audit-orphans.yml

@@ -0,0 +1,22 @@
+name: Audit orphaned benchmark data
+
+on:
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: "0 9 * * 1"
+  workflow_dispatch:
+
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/checkout@v4
+        with:
+          repository: ericchansen/q2mm
+          ref: master
+          path: q2mm-sibling
+      - run: bash scripts/audit-orphans.sh "${GITHUB_WORKSPACE}/q2mm-sibling"

README.md

@@ -71,7 +71,8 @@ For this repo specifically:
   (documentation, paper figure, regression test) belong here.
 
 Run `scripts/audit-orphans.sh` (see below) periodically to catch any
-directories that have lost their references.
+directories that have lost their references.  The same audit now runs
+automatically on every pull request and weekly on Mondays.
 
 ## Auditing for orphaned data
 
@@ -80,6 +81,10 @@ directories that have lost their references.
 scripts/audit-orphans.sh ../q2mm
 ```
 
+The audit also runs automatically in
+[Audit orphaned benchmark data](.github/workflows/audit-orphans.yml) on every
+pull request, weekly on Mondays at 09:00 UTC, and on manual dispatch.
+
 The script walks every `benchmarks/<system>/<subdir>/` and searches the
 q2mm checkout (`docs/`, `test/`, `q2mm/`, `scripts/`, `examples/`) for
 references to that path.  Any subdirectory without a reference is