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/subnet.go

@@ -18,97 +18,27 @@
 package subnet
 
 import (
-	"bytes"
-	"encoding/json"
 	"errors"
-	"fmt"
-	"io"
-	"mime/multipart"
 	"net/http"
-	"time"
-
-	xhttp "github.com/minio/minio/internal/http"
 )
 
 const (
-	respBodyLimit = 1 << 20 // 1 MiB
-
 	// LoggerWebhookName - subnet logger webhook target
 	LoggerWebhookName = "subnet"
 )
 
+var errSiloSubnetDisabled = errors.New("MinIO SUBNET integration is disabled in Silo")
+
 // Upload given file content (payload) to specified URL
 func (c Config) Upload(reqURL string, filename string, payload []byte) (string, error) {
-	if !c.Registered() {
-		return "", errors.New("Deployment is not registered with SUBNET. Please register the deployment via 'mc license register ALIAS'")
-	}
-
-	var body bytes.Buffer
-	writer := multipart.NewWriter(&body)
-	part, e := writer.CreateFormFile("file", filename)
-	if e != nil {
-		return "", e
-	}
-
-	if _, e = part.Write(payload); e != nil {
-		return "", e
-	}
-	writer.Close()
-
-	r, e := http.NewRequest(http.MethodPost, reqURL, &body)
-	if e != nil {
-		return "", e
-	}
-	r.Header.Add("Content-Type", writer.FormDataContentType())
-
-	return c.submitPost(r)
+	return "", errSiloSubnetDisabled
 }
 
-func (c Config) submitPost(r *http.Request) (string, error) {
-	configLock.RLock()
-	r.Header.Set(xhttp.SubnetAPIKey, c.APIKey)
-	configLock.RUnlock()
-	r.Header.Set(xhttp.MinioDeploymentID, xhttp.GlobalDeploymentID)
-
-	client := &http.Client{
-		Timeout:   10 * time.Second,
-		Transport: c.transport,
-	}
-
-	resp, err := client.Do(r)
-	if err != nil {
-		return "", err
-	}
-	defer xhttp.DrainBody(resp.Body)
-
-	respBytes, err := io.ReadAll(io.LimitReader(resp.Body, respBodyLimit))
-	if err != nil {
-		return "", err
-	}
-	respStr := string(respBytes)
-
-	if resp.StatusCode == http.StatusOK {
-		return respStr, nil
-	}
-
-	return respStr, fmt.Errorf("SUBNET request failed with code %d and error: %s", resp.StatusCode, respStr)
+func (c Config) submitPost(_ *http.Request) (string, error) {
+	return "", errSiloSubnetDisabled
 }
 
 // Post submit 'payload' to specified URL
 func (c Config) Post(reqURL string, payload any) (string, error) {
-	if !c.Registered() {
-		return "", errors.New("Deployment is not registered with SUBNET. Please register the deployment via 'mc license register ALIAS'")
-	}
-	body, err := json.Marshal(payload)
-	if err != nil {
-		return "", err
-	}
-	r, err := http.NewRequest(http.MethodPost, reqURL, bytes.NewReader(body))
-	if err != nil {
-		return "", err
-	}
-
-	r.Header.Set("Content-Type", "application/json")
-
-	return c.submitPost(r)
+	return "", errSiloSubnetDisabled
 }