Refactor: Centralize template loading and improve error handling

- Introduced helpers.LoadTemplateFiles() for consistent layout + topbar rendering
- Replaced repeated template.ParseFiles() calls across handlers
- Created generic RenderError(w, r, statusCode) helper
- Replaced old Render403 with flexible RenderError
- Updated AdminOnly middleware to render 403 errors with context
- Added 500.html template for graceful panic fallback
- Prepared structure for future error codes (404, 429, etc.)

handlers/admin/draws.go

@@ -2,7 +2,6 @@ package handlers
 
 import (
 	"database/sql"
-	"html/template"
 	"log"
 	"net/http"
 
@@ -31,10 +30,8 @@ func NewDrawHandler(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		tmpl := template.Must(template.New("new_draw").Funcs(helpers.TemplateFuncs()).ParseFiles(
-			"templates/layout.html",
-			"templates/admin/draws/new_draw.html",
-		))
+		tmpl := helpers.LoadTemplateFiles("new_draw", "templates/admin/draws/new_draw.html")
+
 		tmpl.ExecuteTemplate(w, "layout", context)
 	})
 }
@@ -103,10 +100,8 @@ func ListDrawsHandler(db *sql.DB) http.HandlerFunc {
 
 		context["Draws"] = draws
 
-		tmpl := template.Must(template.New("draw_list").Funcs(helpers.TemplateFuncs()).ParseFiles(
-			"templates/layout.html",
-			"templates/admin/draws/list.html",
-		))
+		tmpl := helpers.LoadTemplateFiles("list.html", "templates/admin/draws/list.html")
+
 		tmpl.ExecuteTemplate(w, "layout", context)
 	})
 }