feat(server): present Silo identity and close the inherited upstream services

Two coupled changes that must land together, because the same files carry both:
the server now identifies itself as Silo, and every path that would have called
home to a MinIO-operated service is closed.

Product identity
- build-constants.go: store name, UA name and startup banner become Silo. The
  Go identifiers (MinioStoreName, MinioBannerName, ...) keep their names on
  purpose - renaming exported symbols would churn the compatibility surface for
  a cosmetic gain, and the rebrand guard freezes that surface.
- main.go, server-startup-msg.go, ftp-server.go and the user-visible log, help
  and error strings across cmd/ and internal/ switch to Silo. Original MinIO
  copyright, LICENSE, NOTICE and CREDITS are untouched; --version now prints
  the upstream copyright, the pgsty modification notice, and the trademark
  policy's approved "based on MinIO technology" attribution.
- api-headers.go: the HTTP Server header becomes "Silo". This is the one
  externally observable identity change, so TestCommonHeadersUseSiloProductName
  pins it - probes that sniff for "MinIO" must move to capability detection.
- Prometheus metric HELP strings keep their MinIO wording. They are part of the
  metrics contract the guard protects, not product copy.

Configuration directory
- config-dir.go: new installs use ~/.silo. If only ~/.minio exists it is still
  read, with a one-time notice and no files moved. If both exist ~/.silo wins
  and an ambiguity warning is emitted; an explicit --config-dir always wins.
  Covered by TestSelectDefaultConfigDir. The internal .minio.sys layout is
  never renamed - this rule applies to the user config directory only.

Upstream service lockdown
- globalInplaceUpdateDisabled is now true at initialization rather than being
  set from MINIO_UPDATE. common-main.go still parses MINIO_UPDATE so upgrading
  nodes do not fail on an unknown key, but warns that the value is ignored;
  there is no way to re-enable the updater. TestInplaceUpdateCannotBeEnabled
  guards that. Without this, an admin with mc could have overwritten
  /usr/bin/silo with an upstream MinIO binary.
- verifyBinary and commitBinary refuse early; the ServerUpdate v1/v2 admin
  routes and the peer-rest update endpoints stay registered and keep returning
  the existing programmatic error, so clients see a stable failure rather than
  a 404.
- MinioReleaseBaseURL and defaultMinisignPubkey are emptied: no dl.min.io
  download root, and upstream's minisign key is no longer a trust root for
  anything this fork ships.
- cmd/callhome.go is deleted and internal/config/subnet/ is reduced to parsing
  its old keys and reporting that the integration is disabled. config-current.go
  warns instead of failing when callhome or SUBNET settings are present, so an
  upgraded node with those keys still starts.
- internal/config/errors.go replaces the MinIO Slack and support entry points
  with Silo documentation and issue links. Error codes and programmatic fields
  are unchanged.

Verified: the compatibility baseline is unchanged except for the deliberate
removal of the /api/health/upload SUBNET route; go build, go vet and the full
cmd/ and internal/ unit suites pass; a locally built binary starts, serves
S3/Admin/metrics on the unchanged /minio/* routes, answers with Server: Silo,
and falls back to a pre-existing ~/.minio with the expected notice.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cmd/config-dir.go

@@ -20,13 +20,16 @@ package cmd
 import (
 	"os"
 	"path/filepath"
+	"sync"
 
 	homedir "github.com/mitchellh/go-homedir"
 )
 
 const (
-	// Default minio configuration directory where below configuration files/directories are stored.
-	defaultMinioConfigDir = ".minio"
+	// New installations use the Silo-branded directory. The legacy directory is
+	// still selected when it is the only existing choice.
+	defaultSiloConfigDir = ".silo"
+	legacyMinioConfigDir = ".minio"
 
 	// Directory contains below files/directories for HTTPS configuration.
 	certsDir = "certs"
@@ -41,33 +44,56 @@ const (
 	privateKeyFile = "private.key"
 )
 
+type defaultConfigDirState uint8
+
+const (
+	defaultConfigDirNew defaultConfigDirState = iota
+	defaultConfigDirLegacy
+	defaultConfigDirAmbiguous
+)
+
 // ConfigDir - points to a user set directory.
 type ConfigDir struct {
 	path string
 }
 
-func getDefaultConfigDir() string {
+func selectDefaultConfigDir(homeDir string) (string, defaultConfigDirState) {
+	siloDir := filepath.Join(homeDir, defaultSiloConfigDir)
+	minioDir := filepath.Join(homeDir, legacyMinioConfigDir)
+	_, siloErr := os.Stat(siloDir)
+	_, minioErr := os.Stat(minioDir)
+
+	siloExists := siloErr == nil || !os.IsNotExist(siloErr)
+	minioExists := minioErr == nil || !os.IsNotExist(minioErr)
+	switch {
+	case siloExists && minioExists:
+		return siloDir, defaultConfigDirAmbiguous
+	case siloExists:
+		return siloDir, defaultConfigDirNew
+	case minioExists:
+		return minioDir, defaultConfigDirLegacy
+	default:
+		return siloDir, defaultConfigDirNew
+	}
+}
+
+func getDefaultConfigDir() (string, defaultConfigDirState) {
 	homeDir, err := homedir.Dir()
 	if err != nil {
-		return ""
+		return "", defaultConfigDirNew
 	}
 
-	return filepath.Join(homeDir, defaultMinioConfigDir)
-}
-
-func getDefaultCertsDir() string {
-	return filepath.Join(getDefaultConfigDir(), certsDir)
-}
-
-func getDefaultCertsCADir() string {
-	return filepath.Join(getDefaultCertsDir(), certsCADir)
+	return selectDefaultConfigDir(homeDir)
 }
 
 var (
+	defaultConfigDirPath, defaultConfigDirSelection = getDefaultConfigDir()
+	defaultConfigDirWarningOnce                     sync.Once
+
 	// Default config, certs and CA directories.
-	defaultConfigDir  = &ConfigDir{path: getDefaultConfigDir()}
-	defaultCertsDir   = &ConfigDir{path: getDefaultCertsDir()}
-	defaultCertsCADir = &ConfigDir{path: getDefaultCertsCADir()}
+	defaultConfigDir  = &ConfigDir{path: defaultConfigDirPath}
+	defaultCertsDir   = &ConfigDir{path: filepath.Join(defaultConfigDirPath, certsDir)}
+	defaultCertsCADir = &ConfigDir{path: filepath.Join(defaultConfigDirPath, certsDir, certsCADir)}
 
 	// Points to current configuration directory -- deprecated, to be removed in future.
 	globalConfigDir = defaultConfigDir