experiment(exp/trufflehog-only): isolate secret-scanner startup_failure

Diagnostic branch. Bisecting a startup_failure that has left this repo with no
secret scanning since 2026-07-17. Will be deleted once the cause is known.

Author: hyperpolymath

.github/workflows/secret-scanner.yml

@@ -3,20 +3,13 @@ name: Secret Scanner
 on:
   pull_request:
   push:
-    branches: [main]
+    branches: [main, 'exp/**']
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 permissions:
   contents: read
 jobs:
-  scan:
-    permissions:
-      contents: read
-      pull-requests: write
-      actions: read
-    uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
-    secrets: inherit
   trufflehog:
     runs-on: ubuntu-latest
     steps:
@@ -26,4 +19,4 @@ jobs:
       - name: TruffleHog Secret Scan
         uses: trufflesecurity/trufflehog@main
         with:
-          extra_args: --only-verified --fail
+          extra_args: --only-verified --fail