refactor(template): delegate handler-level RenderError to helpers package

- Moved core RenderError logic to internal/helpers/template/error.go
- Added thin wrapper method in internal/handlers/template/error.go
- Simplified function signature (no config args, uses InitSiteMeta)
- Preserved architecture: handlers own HTTP layer, helpers supply logic

internal/helpers/template/error.go

@@ -0,0 +1,38 @@
+package helpers
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+
+	"synlotto-website/internal/models"
+)
+
+// RenderError renders an HTML error page (e.g., 404.html, 500.html).
+// It uses TemplateContext which reads site meta from InitSiteMeta().
+func RenderError(w http.ResponseWriter, r *http.Request, statusCode int) {
+	log.Printf("⚙️ RenderError called with status: %d", statusCode)
+
+	ctx := TemplateContext(w, r, models.TemplateData{})
+
+	pagePath := fmt.Sprintf("templates/error/%d.html", statusCode)
+	log.Printf("📄 Checking for template file: %s", pagePath)
+
+	if _, err := os.Stat(pagePath); err != nil {
+		log.Printf("🚫 Template file missing: %s", err)
+		http.Error(w, http.StatusText(statusCode), statusCode)
+		return
+	}
+
+	tmpl := LoadTemplateFiles(fmt.Sprintf("%d.html", statusCode), pagePath)
+
+	w.WriteHeader(statusCode)
+	if err := tmpl.ExecuteTemplate(w, "layout", ctx); err != nil {
+		log.Printf("❌ Failed to render error page layout: %v", err)
+		http.Error(w, http.StatusText(statusCode), statusCode)
+		return
+	}
+
+	log.Println("✅ Successfully rendered error page")
+}