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/windows-free-tests.yml

@@ -31,6 +31,10 @@ concurrency:
   group: windows-free-${{ github.event.pull_request.number || github.run_id }}
   cancel-in-progress: true
 
+# Test-only lane — no token writes.
+permissions:
+  contents: read
+
 jobs:
   windows-free-tests:
     # Ubicloud Windows runner (same provider as the Linux evals workflow).