feat: tunnel JWT auth

Tunnel method now requires Bearer JWT (HMAC-HS256) in gRPC metadata.
   - internal/auth: pure-stdlib verifier + issuer + revoked-jti list
   - internal/tunnel: per-target rate limiter + egress allowlist with
     wildcard support + crypto/rand frame padding to {1KB, 4KB, 16KB}
   - cmd/server reads /etc/stats-gateway/{jwt.key,tunnel.yaml,revoked.txt}
     via --config-dir flag
   - cmd/issue-token Go binary wraps auth.Issue
   - configs/tunnel.yaml example with projectshitpost wildcard


Tests: 13 PASS across 5 packages.

cmd/server/main.go

@@ -1,20 +1,27 @@
 package main
 
 import (
+	"bytes"
 	"flag"
 	"log"
 	"net"
+	"os"
+	"path/filepath"
 
 	"google.golang.org/grpc"
+	"gopkg.in/yaml.v3"
 
 	statsv1 "github.com/bergabruh/stats-gateway/gen/stats/v1"
+	"github.com/bergabruh/stats-gateway/internal/auth"
 	"github.com/bergabruh/stats-gateway/internal/service"
 	"github.com/bergabruh/stats-gateway/internal/storage"
+	"github.com/bergabruh/stats-gateway/internal/tunnel"
 )
 
 func main() {
 	addr := flag.String("addr", "127.0.0.1:50051", "listen address")
 	dbPath := flag.String("db", "/var/lib/stats-gateway/stats.db", "sqlite path")
+	cfgDir := flag.String("config-dir", "/etc/stats-gateway", "config dir (jwt.key, tunnel.yaml, revoked.txt)")
 	flag.Parse()
 
 	st, err := storage.Open(*dbPath)
@@ -23,15 +30,41 @@ func main() {
 	}
 	defer st.Close()
 
+	secret, err := os.ReadFile(filepath.Join(*cfgDir, "jwt.key"))
+	if err != nil {
+		log.Fatalf("read jwt.key: %v", err)
+	}
+	secret = bytes.TrimSpace(secret)
+
+	cfgBytes, err := os.ReadFile(filepath.Join(*cfgDir, "tunnel.yaml"))
+	if err != nil {
+		log.Fatalf("read tunnel.yaml: %v", err)
+	}
+	var tunnelCfg struct {
+		Egress tunnel.EgressConfig `yaml:"egress"`
+	}
+	if err := yaml.Unmarshal(cfgBytes, &tunnelCfg); err != nil {
+		log.Fatalf("parse tunnel.yaml: %v", err)
+	}
+
+	revoked, err := auth.LoadRevokedFile(filepath.Join(*cfgDir, "revoked.txt"))
+	if err != nil {
+		log.Fatalf("load revoked: %v", err)
+	}
+
+	verifier := auth.NewVerifier(secret, revoked)
+	handler := tunnel.NewHandler(tunnelCfg.Egress)
+
 	lis, err := net.Listen("tcp", *addr)
 	if err != nil {
 		log.Fatalf("listen: %v", err)
 	}
 
 	srv := grpc.NewServer()
-	statsv1.RegisterSpeedStatusServer(srv, service.New(st))
+	statsv1.RegisterSpeedStatusServer(srv, service.New(st, verifier, handler))
 
-	log.Printf("stats-gateway listening on %s", *addr)
+	log.Printf("stats-gateway listening on %s (egress=%d targets, rate=%.0fmbps)",
+		*addr, len(tunnelCfg.Egress.Allowed), tunnelCfg.Egress.RateMbps)
 	if err := srv.Serve(lis); err != nil {
 		log.Fatalf("serve: %v", err)
 	}