docs(ocr): clarify entrypoint comment and add manual run hint for skipped test

- entrypoint.sh: replace "cross-job ground-truth leakage" with plain
  "Remove stale partial downloads left by a previous docker-kill"
- test_tmpdir_is_inside_persistent_cache_volume: add docker exec command
  so future developers know how to run this deployment-contract test

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ocr-service/entrypoint.sh

@@ -3,8 +3,7 @@ set -euo pipefail
 
 # Ensure TMPDIR exists on the persistent cache volume (created by the volume-init
 # container, but guaranteed here for fresh volumes and bare docker-run usage).
-# Orphaned fragments from prior docker-kill during model downloads are cleared
-# on startup to prevent cross-job ground-truth leakage (Surya staging files).
+# Remove stale partial downloads left by a previous docker-kill.
 mkdir -p "${TMPDIR:-/tmp}"
 find "${TMPDIR:-/tmp}" -mindepth 1 -mtime +1 -delete 2>/dev/null || true