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>

internal/config/subnet/config.go

@@ -29,11 +29,6 @@ import (
 	xnet "github.com/minio/pkg/v3/net"
 )
 
-const (
-	baseURL    = "https://subnet.min.io"
-	baseURLDev = "http://localhost:9000"
-)
-
 // DefaultKVS - default KV config for subnet settings
 var DefaultKVS = config.KVS{
 	config.KV{
@@ -70,29 +65,21 @@ type Config struct {
 
 var configLock sync.RWMutex
 
-// Registered indicates if cluster is registered or not
+// Registered reports false because Silo does not use MinIO SUBNET. The
+// inherited credentials remain parseable for configuration compatibility.
 func (c *Config) Registered() bool {
-	configLock.RLock()
-	defer configLock.RUnlock()
-
-	return len(c.APIKey) > 0
+	return false
 }
 
 // ApplyEnv - applies the current subnet config to Console UI specific environment variables.
 func (c *Config) ApplyEnv() {
-	configLock.RLock()
-	defer configLock.RUnlock()
-
-	if c.License != "" {
-		os.Setenv("CONSOLE_SUBNET_LICENSE", c.License)
-	}
-	if c.APIKey != "" {
-		os.Setenv("CONSOLE_SUBNET_API_KEY", c.APIKey)
-	}
-	if c.Proxy != "" {
-		os.Setenv("CONSOLE_SUBNET_PROXY", c.Proxy)
-	}
-	os.Setenv("CONSOLE_SUBNET_URL", c.BaseURL)
+	// Do not expose inherited commercial-service credentials or an endpoint to
+	// the embedded Console. These names are outputs, not the MINIO_* input
+	// compatibility surface.
+	os.Unsetenv("CONSOLE_SUBNET_LICENSE")
+	os.Unsetenv("CONSOLE_SUBNET_API_KEY")
+	os.Unsetenv("CONSOLE_SUBNET_PROXY")
+	os.Unsetenv("CONSOLE_SUBNET_URL")
 }
 
 // Update - in-place update with new license and registration information.
@@ -103,15 +90,12 @@ func (c *Config) Update(ncfg Config, isDevEnv bool) {
 	c.License = ncfg.License
 	c.APIKey = ncfg.APIKey
 	c.Proxy = ncfg.Proxy
-	c.transport = ncfg.transport
-	c.BaseURL = baseURL
+	c.transport = nil
+	c.BaseURL = ""
 
-	if isDevEnv {
-		c.BaseURL = os.Getenv("_MINIO_SUBNET_URL")
-		if c.BaseURL == "" {
-			c.BaseURL = baseURLDev
-		}
-	}
+	// Retain the hidden compatibility input but deliberately ignore its value.
+	_ = os.Getenv("_MINIO_SUBNET_URL")
+	_ = isDevEnv
 }
 
 // LookupConfig - lookup config and override with valid environment settings if any.