CI: add least-privilege permissions to GitHub Actions workflows

Add explicit workflow-level permissions blocks to resolve CodeQL
actions/missing-workflow-permissions alerts. Scopes are derived from
workflow operations (git push, artifact upload, Danger, release lanes).

Refs: APPSEC-164

Author: peter-matkovski

.github/workflows/pana.yaml

@@ -11,6 +11,10 @@ on:
     branches:
       - master
 
+permissions:
+  contents: read
+  pull-requests: read
+
 jobs:
   faye_dart:
     runs-on: ubuntu-latest