fix: graceful HTTP server shutdown on SIGINT/SIGTERM

Replace router.Run() with explicit http.Server + Shutdown() so the
process exits cleanly when context is cancelled.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

cmd/bridge/main.go

@@ -3,10 +3,12 @@ package main
 import (
 	"context"
 	"log/slog"
+	"net/http"
 	"os"
 	"os/signal"
 	"sync"
 	"syscall"
+	"time"
 
 	"thuanle.me/claw-email-bridge/internal/ai_client"
 	"thuanle.me/claw-email-bridge/internal/api"
@@ -62,16 +64,30 @@ func main() {
 	// Start HTTP server with SMTP egress on callback.
 	smtpSender := mail.NewSMTPSender(cfg, db)
 	router := api.NewRouter(db, cfg.BridgeCallbackToken, smtpSender.SendReplyFunc())
+	srv := &http.Server{Addr: cfg.ListenAddr, Handler: router}
+
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
 		slog.Info("starting HTTP server", "addr", cfg.ListenAddr)
-		if err := router.Run(cfg.ListenAddr); err != nil {
+		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
 			slog.Error("server exited with error", "error", err)
 			cancel()
 		}
 	}()
 
+	// Graceful shutdown: wait for context cancel then shutdown HTTP server.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-ctx.Done()
+		shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer shutdownCancel()
+		if err := srv.Shutdown(shutdownCtx); err != nil {
+			slog.Error("server shutdown error", "error", err)
+		}
+	}()
+
 	wg.Wait()
 	slog.Info("bridge stopped")
 }