build: prepare the 20260903 dependency release

[Vonng]

Summary

• build MC with Go 1.27.1 across go.mod, CI, dependency checks, and the development container
• consume the released github.com/pgsty/silo-pkg/v3 v3.13.2
• update every dependency used by the client or its tests, including x/crypto v0.56.0 and gRPC v1.83.2
• retain the intentional upstream minio/pkg v3.6.1, tablewriter v0.0.5, go-systemd v22.6.0, and latest-upstream-minio-go compatibility selections
• regenerate CREDITS from the release binary dependency closure

Local validation

• go mod tidy -diff
• go mod verify
• go test ./... -count=1
• make test-race
• make crosscompile
• go run ./buildscripts/check-dependency-floors
• govulncheck ./... — no reachable vulnerabilities
• OSV query over packages compiled by the client and its tests — only the non-imported, no-fixed-version x/crypto/openpgp module advisory remains
• actionlint and git diff --check

No release tag is created by this PR. The release will be tagged only after required CI, exact-main-SHA CI, and the requested Claude Fable 5.1 xhigh adversarial acceptance review all pass.