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/manualtriggers.go

@@ -3,7 +3,6 @@ package handlers
 import (
 	"database/sql"
 	"fmt"
-	"html/template"
 	"log"
 	"net/http"
 	"net/url"
@@ -18,7 +17,6 @@ func AdminTriggersHandler(db *sql.DB) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		context := helpers.TemplateContext(w, r, models.TemplateData{})
 
-		// Inject flash message if available
 		if flash := r.URL.Query().Get("flash"); flash != "" {
 			context["Flash"] = flash
 		}
@@ -69,16 +67,11 @@ func AdminTriggersHandler(db *sql.DB) http.HandlerFunc {
 				flashMsg = "⚠️ Unknown action."
 			}
 
-			// Redirect back with flash message
 			http.Redirect(w, r, "/admin/triggers?flash="+url.QueryEscape(flashMsg), http.StatusSeeOther)
 			return
 		}
 
-		// Render the admin trigger page
-		tmpl := template.Must(template.New("").Funcs(helpers.TemplateFuncs()).ParseFiles(
-			"templates/layout.html",
-			"templates/admin/triggers.html",
-		))
+		tmpl := helpers.LoadTemplateFiles("triggers.html", "templates/admin/triggers.html")
 
 		err := tmpl.ExecuteTemplate(w, "layout", context)
 		if err != nil {