infra (buckets.py): add cc.public / cc.institutes / cc.admin to the bucket
provisioner alongside cc.examboards; make initialize_buckets idempotent
(already-exists treated as success). Bucket provisioning stays in infra init.
new (seed_exam_corpus.py): manifest-driven loader scaffold that USES the buckets
(does not create them) — validate -> upload to cc.examboards (canonical path) ->
upsert eb_specifications/eb_exams -> optional user test subset -> optional
--first-sweep auto-map pass. TODOs marked for the gathering task to complete.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
