fix/ci: resolve all golangci-lint static check failures; drop revive

[johnramsden]

Description

Address every failure reported by golangci-lint under make check-static and add a static-checks CI job so regressions are caught automatically.

errcheck:

• Propagate json.Unmarshal error in ceph/config.go
• Capture and propagate snapRestart error in ceph/services.go
• Check clientConfigUpdate return value in api/client_configs.go handlers
• Check configChangeRefresh return value in api/configs.go handlers
• Check SetAPIObjectID return value in api/ops_replication.go
• Log errors from fire-and-forget goroutines in api/client_configs.go and api/configs.go (adds logger import to configs.go)
• Suppress unchecked errors with _ = in test SetupTest helpers (tests/testutils.go, common/storage_test.go, ceph/services_test.go)
• Use _ = for cobra MarkFlagRequired calls in pool.go, replication_demote.go, replication_disable_cephfs.go, replication_enable_cephfs.go, replication_enable_rbd.go, replication_promote.go

unused:

• Delete unused functions: cephFSSnapshotMirrorDisableVolume, verifyMgrModuleEnabled, enableCephFSMgrModules, rgwCreateServiceDatabase
• Remove unused struct fields: cmdLogSetLevel.logLevel, cmdReplicationList.{poolName,json}
• Clean up now-orphaned imports in manager.go (strings, constants) and rgw.go (database/sql, database)

staticcheck:

• Remove deprecated rand.Seed init() in cmd/microcephd/main.go; drop math/rand and time imports
• Replace golang.org/x/crypto/ssh/terminal with golang.org/x/term in remote_list.go, replication_list_rbd.go, replication_status_rbd.go
• Replace fmt.Errorf(errStr) with errors.New(errStr) in disk_add.go
• Pass context.TODO() instead of nil to slog Logger.Enabled in clilogger/clilogger.go and logger/logger.go
• Remove dead response append loop in ceph/cephfs_volume.go (SA4010)

gosimple:

• Replace fmt.Sprintf("%s", volume) with string(volume) in cephfs_mirror.go

ineffassign:

• Remove duplicate ServicePlacementHandler call in ceph/service_placement_nfs_test.go whose result was immediately overwritten before being checked

Remove revive from Makefile check-static target:

• golangci-lint already covers the issues that matter (correctness, real bugs); revive adds only cosmetic style rules that overlap with golint and can be added back via .golangci.yml incrementally if desired

Add static-checks CI job (.github/workflows/tests.yml):

• Mirrors the existing unit-tests job setup (ubuntu-24.04, dqlite PPA, Go 1.22) and runs make check-static on every push and pull request

Fixes #675

Type of change

Delete options that are not relevant.

• Clean code (code refactor, test updates; does not introduce functional changes)

Contributor checklist

Please check that you have:

• self-reviewed the code in this PR
• added code comments, particularly in less straightforward areas
• checked and added or updated relevant documentation
• checked and added or updated relevant release notes
• added tests to verify effectiveness of this change

[sabaini]

Hey @johnramsden great cleanup, thanks! One mechanical comment per convention we avoid the one line assing/test for better maintainability and readability