Add Spinner, a Minecraft hostname-routing reverse proxy

Routes Java Edition connections by the hostname in the handshake, with
wildcard domains, backend failover, PROXY protocol v2, cached server-list
status from health probes, hot-reloaded config, and an admin page and
metrics endpoint. Includes CI, tagged releases and a container image.

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

internal/router/router.go

@@ -0,0 +1,60 @@
+// Package router maps the hostname a client typed to a configured server.
+package router
+
+import (
+	"sort"
+	"strings"
+
+	"git.veillax.com/Veillax/spinner/internal/config"
+)
+
+type Router struct {
+	exact map[string]*config.Server
+	wild  []wildcard
+}
+
+type wildcard struct {
+	suffix string // ".example.com"
+	srv    *config.Server
+}
+
+// Normalize lowercases a handshake host and strips the trailing dot and any
+// Forge "\0FML\0" suffix.
+func Normalize(host string) string {
+	if i := strings.IndexByte(host, 0); i >= 0 {
+		host = host[:i]
+	}
+	return strings.ToLower(strings.TrimRight(host, "."))
+}
+
+// New builds a router. Exact domains win; wildcards (*.example.com) match any
+// depth of subdomain but not the apex, and longer suffixes win over shorter.
+func New(cfg *config.Config) *Router {
+	r := &Router{exact: map[string]*config.Server{}}
+	for i := range cfg.Servers {
+		s := &cfg.Servers[i]
+		for _, d := range s.Domains {
+			d = strings.ToLower(strings.TrimRight(d, "."))
+			if rest, ok := strings.CutPrefix(d, "*."); ok {
+				r.wild = append(r.wild, wildcard{"." + rest, s})
+			} else if _, dup := r.exact[d]; !dup {
+				r.exact[d] = s
+			}
+		}
+	}
+	sort.SliceStable(r.wild, func(i, j int) bool { return len(r.wild[i].suffix) > len(r.wild[j].suffix) })
+	return r
+}
+
+func (r *Router) Match(host string) *config.Server {
+	host = Normalize(host)
+	if s, ok := r.exact[host]; ok {
+		return s
+	}
+	for _, w := range r.wild {
+		if strings.HasSuffix(host, w.suffix) && len(host) > len(w.suffix) {
+			return w.srv
+		}
+	}
+	return nil
+}