ci(staffml): trigger preview-dev on edits to its own + reusable workflows

The push paths only listed content paths (interviews/staffml/**,
vault questions/chains/schema). When a CI fix landed in any of the
three staffml-* workflow files themselves, the preview-dev workflow
didn't auto-trigger on the push that fixed it — leaving the README
badge stuck on the previous (red) push run until someone happened
to push an unrelated change to interviews/staffml/.

Surfaced this hour: the concurrency-group fix in 2a61ece3f corrected
the actual workflow_call cancellation bug, but the badge stayed red
because that fix only touched .github/workflows/staffml-validate-*.yml.

Add the three workflow file paths to the push trigger so a CI-only
fix re-runs the preview pipeline and updates the badge directly.

.github/workflows/staffml-preview-dev.yml

@@ -50,6 +50,14 @@ on:
       - 'interviews/vault/questions/**'
       - 'interviews/vault/chains.json'
       - 'interviews/vault/schema/**'
+      # Re-run on edits to this workflow or the reusable validate
+      # workflows it calls — without these paths, a CI fix to any
+      # staffml workflow doesn't re-run the badge-driving job, so
+      # the README badge stays red until the next unrelated push to
+      # interviews/staffml/**.
+      - '.github/workflows/staffml-preview-dev.yml'
+      - '.github/workflows/staffml-validate-dev.yml'
+      - '.github/workflows/staffml-validate-vault.yml'
 
 permissions:
   contents: read