refactor(ecstore): drop the client shim, import rustfs-s3-client directly (#6668)

* refactor(ecstore): drop the client shim, import rustfs-s3-client directly

Completes the migration window opened by the rustfs-s3-client extraction (rustfs/backlog#1842 PR3): every consumer now imports the client crate directly and the crate::client shim is deleted.

- All in-crate crate::client:: paths (tier warm backends, tier core, lifecycle tier_sweeper, replication storage boundary, set_disk) now import rustfs_s3_client::* directly; crates/ecstore/src/client/mod.rs and the lib.rs mod client declaration are gone.
- The two server-side modules historically misfiled under client/ move to their real homes: object_api_utils.rs to crates/ecstore/src/object_api/ (it builds engine-side object readers/writers), and object_handlers_common.rs to crates/ecstore/src/bucket/lifecycle/ (it is the lifecycle noncurrent-version cleanup helper). The latter now routes its replication calls through the lifecycle replication_sink boundary (schedule_delete wrapper and the sink's ReplicationObjectBridge re-export), as the lifecycle guard requires.
- The ecstore public facade drops api::client: object_api_utils is exposed as api::object_api_utils, and the rustfs crate takes admin_handler_utils (AdminError) from rustfs-s3-client directly (new dependency).
- Guard updates: the migration guard no longer pins mod client in ecstore's lib.rs or the admin_handler_utils facade module (it pins the new api::object_api_utils facade instead), and the module-lint register follows object_api_utils.rs to its new path.

Verification: cargo check -p rustfs-ecstore --all-targets and -p rustfs; cargo fmt --all; tier/transition/lifecycle-focused nextest (626 passed) and the decommission/rebalance/heal families in a filtered run (603 passed; the full-suite parallel run only fails on this machine's known decommission/rebalance baseline flakes, which pass in filtered reruns and fail identically on pristine origin/main); layer/migration/s3s/logging/error-format/doc-path guard scripts all pass.

* docs(architecture): record the S3 client extraction and reword invariant 4 (#6669)

Closes the documentation step of rustfs/backlog#1842. ARCHITECTURE.md invariant 4 now states the serving-vs-consuming distinction the adversarial ruling asked for: ecstore must not serve HTTP/S3 wire types, while consuming remote S3 endpoints is a legitimate engine capability that lives in the extracted rustfs-s3-client crate. The violation note is updated from the pre-extraction snapshot (58 files, embedded client) to the current ratcheted state (shrink-only S3S_ECSTORE_FILES_BASELINE in scripts/check_s3s_footprint.sh, object_lock converted first), and the crate map gains s3-client. ecstore-module-split-plan.md gets the client-directory entry the plan was missing: a Current Shape row and a completed-extraction section describing the pure-move + shim + direct-import sequence and the re-homing of the two misfiled server-side modules.

ARCHITECTURE.md

@@ -93,7 +93,7 @@ refactors.
 | Domain | Current workspace crates | Responsibility |
 |--------|--------------------------|----------------|
 | Foundation | `checksums`, `common`, `config`, `data-usage`, `heal-contracts`, `scanner-contracts`, `utils` | Shared configuration, data-usage models, heal/scanner domain contracts, utilities, and checksums. |
-| I/O and storage | `concurrency`, `ecstore`, `filemeta`, `heal`, `io-core`, `io-metrics`, `lifecycle`, `lock`, `object-capacity`, `object-data-cache`, `replication`, `rio`, `rio-v2`, `scanner`, `storage-api` | Erasure-coded object storage, metadata, recovery, lifecycle, replication, locking, cache, and I/O pipelines. |
+| I/O and storage | `concurrency`, `ecstore`, `filemeta`, `heal`, `io-core`, `io-metrics`, `lifecycle`, `lock`, `object-capacity`, `object-data-cache`, `replication`, `rio`, `rio-v2`, `s3-client`, `scanner`, `storage-api` | Erasure-coded object storage, metadata, recovery, lifecycle, replication, locking, cache, I/O pipelines, and the engine-side S3 client for remote tier/transition targets. |
 | Security and identity | `credentials`, `crypto`, `iam`, `keystone`, `kms`, `policy`, `security-governance`, `signer`, `tls-runtime`, `trusted-proxies` | Credentials, authentication, authorization, encryption, key management, TLS, and security contracts. |
 | Protocols and contracts | `extension-schema`, `madmin`, `protos`, `protocols`, `s3-ops`, `s3-types`, `s3select-api`, `s3select-query` | Admin, inter-node, S3, S3 Select, and optional protocol contracts. |
 | Operations and integration | `audit`, `notify`, `obs`, `targets`, `zip` | Auditing, observability, event delivery, notification targets, and archive support. |
@@ -138,15 +138,19 @@ default build (lifecycle:
      `BackpressureSettings` copy that lingered in io-metrics was removed
      (rustfs/backlog#1833).
 
-4. **ecstore does not know about HTTP or S3 protocol details.** It operates on
-   storage-level abstractions (objects, buckets, disks, pools).
-   - ⚠️ VIOLATED: 58 files under `crates/ecstore/src` reference `s3s`
-     (`rg -l 's3s' crates/ecstore/src | wc -l`), `crates/ecstore/src/client/`
-     is a ~9.4K-line embedded S3 HTTP client, and `crates/ecstore/Cargo.toml`
-     depends on `s3s`, `http`, `hyper`/`hyper-util`/`hyper-rustls`, and
-     `reqwest`. Target state: the engine's need to act as an S3 client
-     (tiering, replication targets) is served by an extracted client crate,
-     and ecstore holds no wire or DTO types.
+4. **ecstore does not *serve* HTTP or the S3 wire protocol.** It operates on
+   storage-level abstractions (objects, buckets, disks, pools) and holds no
+   wire or DTO types of the serving surface. *Consuming* remote S3-compatible
+   endpoints (ILM tier warm backends, transition targets) is a legitimate
+   engine capability, but it lives in the dedicated `rustfs-s3-client` crate
+   (`crates/s3-client`, extracted from the formerly embedded
+   `crates/ecstore/src/client/` by rustfs/backlog#1842), not inside ecstore.
+   - ⚠️ PARTIALLY VIOLATED: serving-side `s3s` references remain in ecstore
+     (bucket metadata/replication/lifecycle DTOs and error mapping). The
+     count is ratcheted shrink-only by `scripts/check_s3s_footprint.sh`
+     (`S3S_ECSTORE_FILES_BASELINE`; the `object_lock` module was converted to
+     storage-level types as the first ratchet step). Target state: the
+     baseline reaches zero and ecstore's `Cargo.toml` drops `s3s`.
 
 5. **The `rustfs` binary crate is the only place that wires everything together.**
    Individual crates should be testable in isolation.