feat: the admin Overview shows who is listening, downloads, the library and its disk, and the server's version, uptime and recent errors; a download waiting on you, a client not answering or a full disk count in its verdict (M504 #5627 #5628 #5629 #5630)

The version moves to internal/buildinfo, so /rest/ping reports the build
instead of "dev".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/subsonic/envelope.go

@@ -7,6 +7,8 @@ import (
 	"io"
 	"net/http"
 	"strings"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/buildinfo"
 )
 
 // APIVersion is the Subsonic REST version we advertise. 1.16.1 is the last
@@ -18,9 +20,6 @@ const (
 	XMLNS      = "http://subsonic.org/restapi"
 )
 
-// ServerVersion identifies this build. Overwritten by cmd/minstrel at startup.
-var ServerVersion = "dev"
-
 // Envelope holds the attributes present on every Subsonic response. Concrete
 // response types embed it and add endpoint-specific fields with json+xml tags.
 type Envelope struct {
@@ -48,7 +47,7 @@ func NewEnvelope(status string) Envelope {
 		Status:        status,
 		Version:       APIVersion,
 		Type:          ServerType,
-		ServerVersion: ServerVersion,
+		ServerVersion: buildinfo.Version,
 		OpenSubsonic:  true,
 	}
 }