ci: run e2e smoke subset via nextest e2e-smoke profile (#4674)

ci: run e2e smoke subset via nextest e2e-smoke profile (backlog#1149 ci-4)

The e2e-tests job previously ran a single test (delete_marker_migration
_semantics) out of ~400 in the e2e_test crate. Define a nextest
profile.e2e-smoke whose default-filter selects 17 fast single-node
dependency-free modules (63 tests) and run it in the job, reusing the
downloaded debug binary. The profile is the single wiring mechanism for
e2e tests in CI; admission criteria live in crates/e2e_test/README.md,
and docs/testing/e2e-suite-inventory.md records authoritative per-module
counts from cargo nextest list.

crates/e2e_test/README.md

@@ -0,0 +1,51 @@
+# e2e_test
+
+End-to-end test suite for RustFS. Tests spawn a real `rustfs` binary (see
+`src/common.rs`) and drive it with the AWS SDK.
+
+> This README currently only documents the CI smoke subset (backlog#1149
+> ci-4). The full contributor guide — how to add a case, fixture helpers,
+> `#[ignore]` semantics, harness topologies — is tracked as backlog#1153
+> infra-10 and will extend this file.
+
+## CI smoke subset (`--profile e2e-smoke`)
+
+A subset of this crate runs on every PR via the `e2e-tests` job:
+
+```bash
+cargo nextest run --profile e2e-smoke -p e2e_test
+```
+
+The selection lives in `.config/nextest.toml` under `[profile.e2e-smoke]`
+(`default-filter`). That filter is the **single wiring mechanism** for e2e
+tests in CI — extend it (or add a sibling profile) instead of adding new e2e
+jobs to `ci.yml`.
+
+### Admission criteria for the smoke subset
+
+A test module may join the smoke filter only if every test in it is:
+
+1. **Fast** — single-digit seconds per test; the whole subset must keep the
+   `e2e-tests` job ≤ 20 minutes.
+2. **Single-node** — spawns its own server via
+   `RustFSTestEnvironment`/`start_rustfs_server` on a random port with an
+   isolated temp dir. No `RustFSTestClusterEnvironment`, no fixed ports.
+3. **Dependency-free** — no pre-started server at `localhost:9000`, no Vault,
+   no fixed protocol ports. Tools that may be absent on the runner (e.g.
+   `awscurl`) are acceptable only when the test skips gracefully with a
+   visible log line (see `bucket_policy_check_test.rs`).
+4. **Not `#[ignore]`** — ignored tests are activation work (backlog#1149
+   ci-13 / backlog#1148 ilm-3), not smoke candidates.
+
+Note on `#[serial]`: nextest runs each test in its own process, so
+`serial_test`'s in-process mutex does **not** serialize across tests there
+(see the header of `.config/nextest.toml`). Smoke tests must therefore be
+parallel-safe by construction (random port + isolated temp dir), which the
+current subset is.
+
+### Authoritative test inventory
+
+`docs/testing/e2e-suite-inventory.md` records the per-module test counts as
+listed by `cargo nextest list -p e2e_test`. Regenerate it when adding or
+moving e2e tests so acceptance numbers in the test-strategy issues
+(backlog#1147–#1155) stay auditable.