* s3: share the per-key object authorization across copy and delete
AuthorizeCopySource and AuthorizeObjectDelete both authorize a key the request
URL does not name by evaluating the bucket policy and IAM against a synthetic
per-key request; only the method and action differed. Extract that into
authorizeObjectKeyAction and make the two callers thin wrappers. No behavior
change.
Claude-Session: https://claude.ai/code/session_01Qo7p6VsoWxMo8816ogJFk5
* s3: route POST Object uploads through the shared object authorization
POST Object uploads (presigned-POST / HTML form) authorized the write with only
the coarse per-identity Write action, unlike the other write paths which also
check the resolved object against the bucket policy and IAM. Route POST through
authorizeObjectKeyAction via a new AuthorizeObjectWrite so it is authorized like
the equivalent PUT.
Claude-Session: https://claude.ai/code/session_01Qo7p6VsoWxMo8816ogJFk5
* s3: test POST Object per-key authorization
Drives a signed POST upload and checks the per-key authorization decision for a
denied, permitted, and admin caller.
Claude-Session: https://claude.ai/code/session_01Qo7p6VsoWxMo8816ogJFk5
