test: use Actions token-based inference for doc-freshness (no PAT)

Adds 'copilot-requests: write' so the Copilot engine uses the built-in
GITHUB_TOKEN instead of a COPILOT_GITHUB_TOKEN PAT secret. Requires org
centralized Copilot billing. Temporary push trigger still active for testing.

Author: EMaher

.github/workflows/doc-freshness.lock.yml

@@ -14,6 +14,7 @@ on:
 permissions:
   contents: read
   issues: read
+  copilot-requests: write  # use GitHub Actions token-based inference (no PAT) — requires org centralized Copilot billing
 
 timeout-minutes: 10