Refactor exam start template for improved readability and URL handling

sbas/templates/sbas/exam_start.html

@@ -2,7 +2,7 @@
 
 {% block content %}
 
-    <h2>Start exam: {{exam}}</h2>
+    <h2>Start exam: {{ exam }}</h2>
 
     {% if exam.time_limit %}
         This exam has a time limit of {{ exam.get_time_limit }}. The time will start when you click the Start Exam button below.<br/>
@@ -44,7 +44,10 @@
                     let passcode = $("#passcode-box").val();
 
                     if (Number.isInteger(parseInt(cid))) {
-                        window.location.replace("{% url 'sbas:exam_take' pk=exam.pk sk=0 cid='0000000' passcode='ZZZZZZ' %}".replace("0000000", cid).replace("ZZZZZZ", passcode));
+                        // reverse a URL with safe placeholders and replace them client-side
+                        const template = "{% url 'sbas:exam_take' pk=exam.pk sk=0 cid=0 passcode='0' %}"; // e.g. /sbas/exam/1/0/0/0/take
+                        const url = template.replace('/0/0/take', `/${cid}/${passcode}/take`);
+                        window.location.replace(url);
                     } else {
                         alert("Please enter a valid Candidate ID (CID).")
                     }