membership: panic on startup with GODEBUG=fips140=only due to SHA-1 in cluster/member ID derivation

### Bug report criteria

- [x] This bug report is not security related, security issues should be disclosed privately via security@etcd.io.
- [x] This is not a support request or question, support requests or questions should be raised in the etcd [discussion forums](https://github.com/etcd-io/etcd/discussions).
- [x] You have read the etcd [bug reporting guidelines](https://github.com/etcd-io/etcd/blob/main/Documentation/contributor-guide/reporting_bugs.md).
- [x] Existing open issues along with etcd [frequently asked questions](https://etcd.io/docs/latest/faq) have been checked and this is not a duplicate.

### What happened?

When etcd is built with Go 1.24+ and started with `GODEBUG=fips140=only`, the
process panics on startup. The Go runtime refuses to execute SHA-1 under strict
FIPS 140-3 mode, but etcd uses SHA-1 in two places to derive cluster and member IDs:

- `server/etcdserver/api/membership/cluster.go` (cluster ID derivation via `sha1.Sum`)
- `server/etcdserver/api/membership/member.go` (member ID derivation via `sha1.Sum`)

### What did you expect to happen?

etcd should start cleanly under `GODEBUG=fips140=only`. The SHA-1 in these files
is not used for any security property — it's a deterministic digest used to produce
a ID — but Go's strict FIPS mode refuses to execute SHA-1 regardless of intent.

### How can we reproduce it (as minimally and precisely as possible)?

1. Build etcd from main with Go 1.24 or newer.
2. Run with `GODEBUG=fips140=only` set:
GODEBUG=fips140=only ./bin/etcd
--name node1
--data-dir /tmp/etcd-data
--listen-client-urls http://127.0.0.1:2379
--advertise-client-urls http://127.0.0.1:2379
--listen-peer-urls http://127.0.0.1:2380
--initial-advertise-peer-urls http://127.0.0.1:2380
--initial-cluster node1=http://127.0.0.1:2380

3. Process panics during membership initialization.
panic: crypto/sha1: use of SHA-1 is not allowed in FIPS 140-only mode
goroutine 1 [running]: crypto/sha1.Sum({0x39fd3820a740, 0x21, 0x40}) crypto/sha1/sha1.go:278 +0x145 go.etcd.io/etcd/server/v3/etcdserver/api/membership.computeMemberID(...) go.etcd.io/etcd/server/v3/etcdserver/api/membership/member.go:74 +0x34e ...

### Anything else we need to know?

### Why we cannot just replace SHA-1 with SHA-256

A one-line replacement of `sha1.Sum` with `sha256.Sum256` would compile and
fix the panic, but it changes every cluster ID and member ID. These IDs are:

- Persisted to the WAL on every node
- Written into snapshots
- Exchanged during peer handshakes
- Used to reject cross-cluster traffic ("cluster ID mismatch")

A node built with the new hash cannot rejoin or recover a cluster bootstrapped
with the old hash. This makes a direct swap backward-incompatible for every
existing etcd deployment.

### Related

- Go 1.24 native FIPS 140-3: https://go.dev/doc/security/fips140
- Earlier etcd FIPS question (closed 2022): #14223
- Go-side X25519/FIPS issues: golang/go#75148, golang/go#78298

### Etcd version (please run commands below)

```console
$ etcd --version
etcd Version: 3.7.0-alpha.0
Git SHA: f38159321
Go Version: go1.26.2
Go OS/Arch: linux/amd64

$ etcdctl version
etcdctl version: 3.7.0-alpha.0
API version: 3.7
```

### Etcd configuration (command line flags or environment variables)

```console
GODEBUG=fips140=only ./bin/etcd \
--name node1 \
--data-dir /tmp/etcd-data \
--listen-client-urls http://127.0.0.1:2379 \
--advertise-client-urls http://127.0.0.1:2379 \
--listen-peer-urls http://127.0.0.1:2380 \
--initial-advertise-peer-urls http://127.0.0.1:2380 \
--initial-cluster node1=http://127.0.0.1:2380
```

### Etcd debug information (please run commands below, feel free to obfuscate the IP address or FQDN in the output)

```console
$ etcdctl member list -w table
# N/A — etcd panics on startup before accepting client connections

$ etcdctl --endpoints= endpoint status -w table
# N/A — etcd panics on startup before accepting client connections
```

### Relevant log output

```Shell
panic: crypto/sha1: use of SHA-1 is not allowed in FIPS 140-only mode

goroutine 1 [running]:
crypto/sha1.Sum({0x39fd3820a740, 0x21, 0x40})
crypto/sha1/sha1.go:278 +0x145
go.etcd.io/etcd/server/v3/etcdserver/api/membership.computeMemberID({0x39fd37f7d680, 0x1, 0x39fd3838efa0?}, {0x125a986, 0xc}, 0x0)
go.etcd.io/etcd/server/v3/etcdserver/api/membership/member.go:74 +0x34e
go.etcd.io/etcd/server/v3/etcdserver/api/membership.NewMember({0x7fff03ca5751, 0x5}, {0x39fd37f7d680, 0x1, 0x1}, {0x125a986?, 0x39fd3835e120?}, 0x39fd37f7d680?)
go.etcd.io/etcd/server/v3/etcdserver/api/membership/member.go:52 +0x45
go.etcd.io/etcd/server/v3/etcdserver/api/membership.NewClusterFromURLsMap(0x39fd38256c08?, {0x125a986, 0xc}, 0x39fd38041500, {0x39fd3838f140?, 0x39fd37fd7200?, 0x39fd3838f0d8?})
go.etcd.io/etcd/server/v3/etcdserver/api/membership/cluster.go:84 +0xd8
go.etcd.io/etcd/server/v3/etcdserver.bootstrapNewClusterNoWAL({{0x7fff03ca565f, 0x5}, {{{0x1d7aca0, 0x0, 0x0}, 0x12a05f200, 0x77359400, 0x77359400, 0x165a0bc00, 0x0, ...}, ...}, ...}, ...)
go.etcd.io/etcd/server/v3/etcdserver/bootstrap.go:354 +0x118
go.etcd.io/etcd/server/v3/etcdserver.bootstrapCluster({{0x7fff03ca565f, 0x5}, {{{0x1d7aca0, 0x0, 0x0}, 0x12a05f200, 0x77359400, 0x77359400, 0x165a0bc00, 0x0, ...}, ...}, ...}, ...)
go.etcd.io/etcd/server/v3/etcdserver/bootstrap.go:306 +0x156
go.etcd.io/etcd/server/v3/etcdserver.bootstrap({{0x7fff03ca565f, 0x5}, {{{0x1d7aca0, 0x0, 0x0}, 0x12a05f200, 0x77359400, 0x77359400, 0x165a0bc00, 0x0, ...}, ...}, ...})
go.etcd.io/etcd/server/v3/etcdserver/bootstrap.go:92 +0x8f9
go.etcd.io/etcd/server/v3/etcdserver.NewServer({{0x7fff03ca565f, 0x5}, {{{0x1d7aca0, 0x0, 0x0}, 0x12a05f200, 0x77359400, 0x77359400, 0x165a0bc00, 0x0, ...}, ...}, ...})
go.etcd.io/etcd/server/v3/etcdserver/server.go:295 +0x8b
go.etcd.io/etcd/server/v3/embed.StartEtcd(0x39fd38177c08)
go.etcd.io/etcd/server/v3/embed/etcd.go:260 +0x115f
go.etcd.io/etcd/server/v3/etcdmain.startEtcd(0x39fd3818c900?)
go.etcd.io/etcd/server/v3/etcdmain/etcd.go:181 +0x17
go.etcd.io/etcd/server/v3/etcdmain.startEtcdOrProxyV2({0x39fd37fb6000, 0xf, 0xf})
go.etcd.io/etcd/server/v3/etcdmain/etcd.go:127 +0xf85
go.etcd.io/etcd/server/v3/etcdmain.Main({0x39fd37fb6000, 0xf, 0xf})
go.etcd.io/etcd/server/v3/etcdmain/main.go:40 +0xf3
main.main()
go.etcd.io/etcd/server/v3/main.go:31 +0x28
```