ci(secret-scan): rename caller job key secret-scan -> scan (D243)

Secret-Scan-Floor (D243/D244) requires the context `scan / gitleaks` estate-wide. The caller job key here was `secret-scan`, which emits `secret-scan / gitleaks` and can never satisfy the floor. Rename only; the reusable pin and permissions are unchanged.

actionlint output identical before and after.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0136eszqrQ53Kj7aBH1D4rXK

Author: hyperpolymath

.github/workflows/secret-scanner.yml

@@ -18,7 +18,7 @@ permissions:
   actions: read
   contents: read
 jobs:
-  secret-scan:
+  scan:
     uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@bd0df9ead7faf0cdfe0e13e7966d91e28d0101d4
     secrets: inherit
     permissions: