Durable per-run screenshot store for the morelli review app
(github.com/PCBJam/morelli): after the report step, CI uploads the renders
and a meta.json index (identity, branch/commit, per-shot sha256+dims,
embedded compare summary) to runs/pcbjam/<GITHUB_RUN_ID>/ — 30-day R2
lifecycle; GH artifacts remain the debugging archive. meta.json is written
last as the upload-complete marker. Uses a new optional WRITE keypair
(CI_SCREENSHOTS_S3_WRITE_*); without it the step no-ops, so secretless
callers stay green. R2Store gains putKey() for the non-CAS run keys.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
