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/ticket_handler.go

@@ -3,7 +3,6 @@ package handlers
 import (
 	"database/sql"
 	"fmt"
-	"html/template"
 	"io"
 	"log"
 	"net/http"
@@ -44,10 +43,7 @@ func AddTicket(db *sql.DB) http.HandlerFunc {
 			context["csrfField"] = csrf.TemplateField(r)
 			context["DrawDates"] = drawDates
 
-			tmpl := template.Must(template.New("").Funcs(helpers.TemplateFuncs()).ParseFiles(
-				"templates/layout.html",
-				"templates/account/tickets/add_ticket.html",
-			))
+			tmpl := helpers.LoadTemplateFiles("add_ticket.html", "templates/account/tickets/add_ticket.html")
 
 			err = tmpl.ExecuteTemplate(w, "layout", context)
 			if err != nil {
@@ -362,10 +358,7 @@ func GetMyTickets(db *sql.DB) http.HandlerFunc {
 		context := helpers.TemplateContext(w, r, models.TemplateData{})
 		context["Tickets"] = tickets
 
-		tmpl := template.Must(template.New("").Funcs(helpers.TemplateFuncs()).ParseFiles(
-			"templates/layout.html",
-			"templates/account/tickets/my_tickets.html",
-		))
+		tmpl := helpers.LoadTemplateFiles("my_tickets.html", "templates/account/tickets/my_tickets.html")
 
 		err = tmpl.ExecuteTemplate(w, "layout", context)
 		if err != nil {