docs(6205): last id-less stories in services — a ported-from project name and two "this milestone" references

backup_s3 says what its signing is checked against instead of which of the
operator's projects it was ported from; rulebooks and shape_check state what
the code is for rather than which milestone it belonged to.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/services/backup_s3.py

@@ -1,8 +1,8 @@
 """A small S3 client for sending backups: AWS Signature Version 4 over httpx,
 path-style addressing (endpoint/bucket/key), and the two calls a backup needs.
 
-Ported from FabledSteward's `steward/backup/s3.py`, which is tested against
-the same AWS examples as tests/test_services_backup_s3.py.
+The signing is checked against AWS's published SigV4 examples in
+tests/test_services_backup_s3.py.
 
 Scribe puts and lists; it never deletes. The bucket keeps the history and
 thins it on its own policy, so a key that may only add objects is enough —