fix(ci): grant secret-scanner reusable its requested job permissions (#44)

Estate sweep: the reusable's gitleaks job requests `pull-requests:
write` + `actions: read` (PR summary comments, .git-private-farm#69). A
called workflow cannot exceed the caller's grant, so this wrapper died
at `startup_failure` on every run — at any pin. Root cause and canonical
caller shape fixed in standards#472; proven green on
somethings-fishy#51.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/secret-scanner.yml

@@ -15,5 +15,13 @@ permissions:
 
 jobs:
   scan:
+    # The reusable's gitleaks job requests pull-requests: write (PR
+    # summary comments) and actions: read. A called workflow cannot
+    # exceed the caller's grant - without these, every run dies at
+    # startup_failure. See standards#472.
+    permissions:
+      contents: read
+      pull-requests: write
+      actions: read
     uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
-    secrets: inherit
+    secrets: inherit