feat(screenshots): migrate to new service and delete on push

[jomifepe]

Summary

• Replace the legacy ACL provider with the Obelix screenshot service for variation screenshot uploads (slice add-variation, slice edit-variation)
• Use presigned POST credentials from GET /screenshot/presigned-url and align S3 keys with the new service: {repo}/shared-slices/{sliceId}/{variationId}/{sha1}{ext} (SHA1 digest, dot-separated extension)
• Call POST /screenshot/delete during prismic push when remote slices are removed, matching editor behavior (failures are logged as warnings so the slice delete still completes)
• Improve custom type deletion on push with clearer errors when associated documents block deletion, including links to the type builder and filtered document list

Closes #145

Test plan

• CI passes
• E2E: slice-add-variation and slice-edit-variation screenshot uploads
• E2E: push.serial.test.ts — push deletes a remote slice and cleans up its screenshot files (uses test/fixtures/slice-screenshot.png)
• Manual smoke test with --screenshot on a local PNG

Made with Cursor

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Note

Medium Risk
Swaps presigned-upload and storage-key logic (new host and SHA1 keys) and adds best-effort screenshot deletion during push, which could leave orphaned files if the delete API fails.

Overview
Slice variation screenshot uploads now use the internal screenshot service (api.internal…/screenshot/) instead of acl-provider: presigned POST credentials come from presigned-url, and object keys use a SHA1 content hash (replacing MD5) under {repo}/shared-slices/{sliceId}/{variationId}/….

prismic push calls deleteScreenshots after each remote slice removal (failures are logged as warnings so the slice delete still completes). Serial E2E coverage uploads a screenshot, pushes a local slice delete with --force, and asserts both the slice and its screenshot keys are gone.

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[jomifepe]

This is to match Type Builder (md5 is not native to web), not critical, but not harmful.