refactor(memory): S3-generic store on boto3; RustFS is the tested server (no MinIO naming)

The plane's memory store no longer names one vendor. `MinioStore`/`SdkClient`/
`minio_settings`/`MINIO_KEYS` become `S3Store`/`S3Client`/`s3_settings`/`S3_KEYS`;
the URL scheme is `s3://<bucket>[/<prefix>]` (`s3://` alone uses `S3_BUCKET`); the
settings are `S3_ENDPOINT` (a full URL), `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`,
optional `AWS_SESSION_TOKEN` and `S3_REGION`. The client is boto3 (extra `s3`,
imported lazily): SigV4, path-style addressing, SDK checksum trailers off, paginated
listing, versions and delete markers listed and deleted by version (`purge`, used by
the contract tests' teardown so the bucket keeps nothing of a run).

Behaviour is unchanged: the store never configures its bucket and verifies
versioning, the `runs/` expiry rule, S3 Select and tag reads at startup; no local
fallback; every row carries every queryable field with "" placeholders. The admin
hints read `--endpoint-url "$S3_ENDPOINT"`. The fake client still reproduces RustFS's
two Select failures (unbound leading-row field, null-typed column).

Docs: rustfs.md stays the tested server's setup page (policy JSON unchanged, env
names updated, any S3-compatible store with versioning, lifecycle, tags and Select
works); memory.md, ops/ax/README.md, README.md, steering and the two current spec
designs use the S3 naming. Retired specs and committed measurements are untouched.

Real server (RustFS, OUSAST_MEMORY_TEST_S3=1): test_plane_memory + test_learn_compile
75 passed, 1 skipped. Store copy of the live local store to a temporary prefix: every
count matched (776 row objects, 2982 rows, 22 facts, 788 excerpts, 2601 responses,
2 programs, 1793 index entries), 4190 versions purged afterwards.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/cli.py

@@ -218,7 +218,7 @@ def _main(argv: list[str] | None) -> int:
         const="",
         default=None,
         metavar="STORE",
-        help="also propose rule-status edits from the plane memory store (a directory, file:// or minio:// URL; "
+        help="also propose rule-status edits from the plane memory store (a directory, file:// or s3:// URL; "
         "no value: OUSAST_MEMORY or the default store); off by default",
     )
     improve.add_argument(
@@ -290,7 +290,7 @@ def _main(argv: list[str] | None) -> int:
     plane_normalise = plane_sub.add_parser(
         "memory-normalise", help='rewrite the store\'s rows to the fixed schema (every queryable field, "" where absent); idempotent'
     )
-    plane_normalise.add_argument("--store", help="the store URL (default OUSAST_MEMORY): file:///<path> or minio://<bucket>[/<prefix>]")
+    plane_normalise.add_argument("--store", help="the store URL (default OUSAST_MEMORY): file:///<path> or s3://<bucket>[/<prefix>]")
     plane_normalise.add_argument("--dry-run", action="store_true", help="count what would be rewritten, write nothing")
     plane_engine = plane_sub.add_parser(
         "alerts-engine", help="a Run's `alerts` for PHP and languages quick mode does not cover, from the engine image on this host"