feat: add email notification service with SMTP support

- Create pkg/email package (sender, templates, types)
- SMTP client with TLS, rate limiting, async sending
- HTML email templates with GooSeek branding
- Integrate welcome + password reset emails in auth-svc
- Add limit warning emails (80%/100%) in llm-svc middleware
- Add space invite endpoint with email notification in thread-svc
- Add GetUserEmail helper in JWT middleware
- Add SMTP config to .env, config.go, K8s configmap

Made-with: Cursor

backend/cmd/auth-svc/main.go

@@ -16,6 +16,7 @@ import (
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/gooseek/backend/internal/auth"
 	"github.com/gooseek/backend/pkg/config"
+	"github.com/gooseek/backend/pkg/email"
 	_ "github.com/lib/pq"
 )
 
@@ -73,6 +74,22 @@ func main() {
 
 	authRepo := auth.NewRepository(db)
 
+	emailSender := email.NewSender(email.SMTPConfig{
+		Host:     cfg.SMTPHost,
+		Port:     cfg.SMTPPort,
+		User:     cfg.SMTPUser,
+		Password: cfg.SMTPPassword,
+		From:     cfg.SMTPFrom,
+		TLS:      cfg.SMTPTLS,
+		SiteURL:  cfg.SiteURL,
+		SiteName: cfg.SiteName,
+	})
+	if emailSender.IsConfigured() {
+		log.Println("Email notifications enabled")
+	} else {
+		log.Println("Email notifications disabled (SMTP not configured)")
+	}
+
 	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 	if err := authRepo.RunMigrations(ctx); err != nil {
 		log.Printf("Migration warning: %v", err)
@@ -150,6 +167,10 @@ func main() {
 			return c.Status(500).JSON(fiber.Map{"error": "Failed to generate tokens"})
 		}
 
+		emailSender.SendAsync(func() error {
+			return emailSender.SendWelcome(user.Email, user.Name)
+		})
+
 		return c.Status(201).JSON(tokens)
 	})
 
@@ -331,7 +352,10 @@ func main() {
 		if err == nil && user != nil {
 			token, err := authRepo.CreatePasswordResetToken(c.Context(), user.ID)
 			if err == nil {
-				log.Printf("Password reset token for %s: %s", req.Email, token.Token)
+				resetURL := fmt.Sprintf("%s/reset-password?token=%s", cfg.SiteURL, token.Token)
+				emailSender.SendAsync(func() error {
+					return emailSender.SendPasswordReset(user.Email, user.Name, resetURL)
+				})
 			}
 		}