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/server/server.go

@@ -15,6 +15,7 @@ import (
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/api"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/buildinfo"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/config"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/coverart"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/eventbus"
@@ -232,8 +233,8 @@ func (s *Server) handleHealthz(w http.ResponseWriter, _ *http.Request) {
 	w.WriteHeader(http.StatusOK)
 	_ = json.NewEncoder(w).Encode(map[string]string{
 		"status":             "ok",
-		"version":            ServerVersion,
-		"channel":            ServerChannel,
+		"version":            buildinfo.Version,
+		"channel":            buildinfo.Channel,
 		"min_client_version": MinClientVersion,
 	})
 }

internal/server/version.go

@@ -5,27 +5,5 @@ package server
 // older clients see version_too_old at /healthz and refuse to operate.
 const MinClientVersion = "0.1.0"
 
-// ServerVersion is the build's own version name — YYYY.MM.DD.HHMM, derived
-// from the commit it was built from by ci/version.sh. Defaults to "dev" for
-// local builds; overridden at link time via:
-//
-//	-ldflags="-X 'git.fabledsword.com/bvandeusen/minstrel/internal/server.ServerVersion=2026.09.10.1449'"
-//
-// release.yml passes it through the MINSTREL_VERSION build-arg → Dockerfile
-// ldflag. Surfaced at /healthz so operators can verify which image their
-// container is running without exec'ing into it.
-//
-// This carried the literal strings "main" and "dev" until 2026-09-10, which
-// made every image on a channel report the same thing forever. It stopped
-// being cosmetic when :vYYYY.MM.DD.HHMM image tags were retired (family rule
-// 145): this is now the ONLY thing that says which build is running.
-var ServerVersion = "dev"
-
-// ServerChannel is which line this build came off — "stable" or "dev", or
-// "local" for a plain `docker build`.
-//
-// A SIBLING FIELD, never a suffix inside ServerVersion (family rule 149). The
-// same commit built on both lanes reports the same version and differs only
-// here; folding the two together is what makes a version string stop being
-// comparable.
-var ServerChannel = "local"
+// The build's version and channel live in internal/buildinfo, shared with
+// the Subsonic envelope and the admin Overview (M504).