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/update_test.go

@@ -20,6 +20,7 @@ package cmd
 import (
 	"bytes"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
@@ -35,6 +36,9 @@ import (
 )
 
 func TestDownloadBinaryReturnsOwnedBuffers(t *testing.T) {
+	previousDisabled := globalInplaceUpdateDisabled
+	globalInplaceUpdateDisabled = false
+	t.Cleanup(func() { globalInplaceUpdateDisabled = previousDisabled })
 	previousMaxProcs := runtime.GOMAXPROCS(1)
 	t.Cleanup(func() {
 		runtime.GOMAXPROCS(previousMaxProcs)
@@ -96,6 +100,19 @@ func TestDownloadBinaryReturnsOwnedBuffers(t *testing.T) {
 	}
 }
 
+func TestInplaceUpdateCannotBeEnabled(t *testing.T) {
+	previousDisabled := globalInplaceUpdateDisabled
+	globalInplaceUpdateDisabled = true
+	t.Cleanup(func() { globalInplaceUpdateDisabled = previousDisabled })
+
+	if err := verifyBinary(nil, nil, "", "", nil); !errors.Is(err, errInplaceUpdateDisabled) {
+		t.Fatalf("verifyBinary error = %v, want %v", err, errInplaceUpdateDisabled)
+	}
+	if err := commitBinary(); !errors.Is(err, errInplaceUpdateDisabled) {
+		t.Fatalf("commitBinary error = %v, want %v", err, errInplaceUpdateDisabled)
+	}
+}
+
 func TestMinioVersionToReleaseTime(t *testing.T) {
 	testCases := []struct {
 		version    string
@@ -167,19 +184,11 @@ func TestDownloadURL(t *testing.T) {
 	minioVersion1 := releaseTimeToReleaseTag(UTCNow())
 	durl := getDownloadURL(minioVersion1)
 	if IsDocker() {
-		if durl != "podman pull quay.io/minio/minio:"+minioVersion1 {
-			t.Errorf("Expected %s, got %s", "podman pull quay.io/minio/minio:"+minioVersion1, durl)
-		}
-	} else {
-		if runtime.GOOS == "windows" {
-			if durl != MinioReleaseURL+"minio.exe" {
-				t.Errorf("Expected %s, got %s", MinioReleaseURL+"minio.exe", durl)
-			}
-		} else {
-			if durl != MinioReleaseURL+"minio" {
-				t.Errorf("Expected %s, got %s", MinioReleaseURL+"minio", durl)
-			}
+		if durl != "podman pull docker.io/pgsty/silo:"+minioVersion1 {
+			t.Errorf("Expected %s, got %s", "podman pull docker.io/pgsty/silo:"+minioVersion1, durl)
 		}
+	} else if durl != siloDownloadPage {
+		t.Errorf("Expected %s, got %s", siloDownloadPage, durl)
 	}
 
 	t.Setenv("KUBERNETES_SERVICE_HOST", "10.11.148.5")
@@ -207,19 +216,19 @@ func TestUserAgent(t *testing.T) {
 			envName:     "",
 			envValue:    "",
 			mode:        globalMinioModeFS,
-			expectedStr: fmt.Sprintf("MinIO (%s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET", runtime.GOOS, runtime.GOARCH, globalMinioModeFS),
+			expectedStr: fmt.Sprintf("Silo (%s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET", runtime.GOOS, runtime.GOARCH, globalMinioModeFS),
 		},
 		{
 			envName:     "MESOS_CONTAINER_NAME",
 			envValue:    "mesos-11111",
 			mode:        globalMinioModeErasure,
-			expectedStr: fmt.Sprintf("MinIO (%s; %s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET universe-%s", runtime.GOOS, runtime.GOARCH, globalMinioModeErasure, "dcos", "mesos-1111"),
+			expectedStr: fmt.Sprintf("Silo (%s; %s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET universe-%s", runtime.GOOS, runtime.GOARCH, globalMinioModeErasure, "dcos", "mesos-1111"),
 		},
 		{
 			envName:     "KUBERNETES_SERVICE_HOST",
 			envValue:    "10.11.148.5",
 			mode:        globalMinioModeErasure,
-			expectedStr: fmt.Sprintf("MinIO (%s; %s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET", runtime.GOOS, runtime.GOARCH, globalMinioModeErasure, "kubernetes"),
+			expectedStr: fmt.Sprintf("Silo (%s; %s; %s; %s; source DEVELOPMENT.GOGET DEVELOPMENT.GOGET DEVELOPMENT.GOGET", runtime.GOOS, runtime.GOARCH, globalMinioModeErasure, "kubernetes"),
 		},
 	}