feat(release): version stamping and tag-triggered release workflow

--version/-V on the CLI, version in /api/health via Server.SetVersion,
Makefile/Dockerfile ldflags stamping from git describe, and a release
workflow on v* tags: both binaries for linux/darwin (amd64+arm64) and
windows/amd64 with SHA256SUMS attached to the Gitea release
(idempotent — reuses an existing hand-written release and skips
already-uploaded assets), plus version-tagged Docker images.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

cmd/server/main.go

@@ -13,17 +13,21 @@ import (
 	"gitea.hansenits.com.au/hits/ExploreDNS/web/api"
 )
 
+// version is stamped at build time via -ldflags "-X main.version=...".
+var version = "dev"
+
 func main() {
 	addr := flag.String("addr", ":8080", "listen address (host:port)")
 	flag.Parse()
 
 	srv := api.NewServer(*addr)
+	srv.SetVersion(version)
 	if err := srv.Start(); err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 		os.Exit(1)
 	}
 
-	log.Printf("ExploreDNS API server listening on %s", srv.Addr())
+	log.Printf("ExploreDNS API server %s listening on %s", version, srv.Addr())
 
 	quit := make(chan os.Signal, 1)
 	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)