fix(ci): least-privilege permissions + fork-safe concurrency keys

- evals.yml / evals-periodic.yml evals jobs: explicit contents:read +
  packages:read (container-image pull) and persist-credentials:false —
  the jobs that execute PR-authored code with three provider API keys
  ran on the repo-default token grant with the token written into
  .git/config
- permissions blocks for the 4 workflows that had none (skill-docs,
  make-pdf-gate, windows-free-tests, windows-setup-e2e)
- fork-safe concurrency keys: actionlint, skill-docs, make-pdf-gate,
  windows-setup-e2e switch from head_ref to PR-number keying — a bare
  branch name carries no fork prefix, so same-name branches from two
  forks shared one group and cancelled each other's runs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/evals-periodic.yml

@@ -68,6 +68,11 @@ jobs:
   evals:
     runs-on: ubicloud-standard-8
     needs: build-image
+    # Least privilege (mirrors evals.yml): read-only contents, packages:read
+    # for the container-image pull.
+    permissions:
+      contents: read
+      packages: read
     container:
       image: ${{ needs.build-image.outputs.image-tag }}
       credentials:
@@ -110,6 +115,7 @@ jobs:
       - uses: actions/checkout@v7
         with:
           fetch-depth: 0
+          persist-credentials: false
 
       - name: Fix bun temp
         run: |