Look pictures (a person's attachments) archive to the BlobStore #4546

Split from #4489 (step 2 of #4481), which built src/blob/store.ts (BlobStore; docs/BLOBS.md).

Looks (src/core/looks.ts) are the pictures of an environment, including the ones a person attaches. They are files under the data dir. Write each picture to the BlobStore by a content key, put(key, Bun.file(path)). Serve it from there through the forge, or with a short presigned GET when the store is a bucket (the access check happens before the URL is signed). deleteLooks deletes the objects along with the rows.

• Test: a look is written, served and deleted through a dirStore. A private app's picture is never presigned for someone who cannot read the app.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.