Standardize: Convert 7 high-priority $conn->query() to prepared statements

Converted queries in:
- functions.php:
  * getTripCount() - Hardcoded query
  * getAvailableSpaces() - Two queries using $trip_id parameter (HIGH PRIORITY)

- blog.php:
  * Main blog list query - Hardcoded 'published' status

- course_details.php:
  * Driver training courses query - Hardcoded course type

- driver_training.php:
  * Future driver training dates query - Hardcoded course type

- events.php:
  * Upcoming events query - Hardcoded date comparison

- index.php:
  * Featured trips query - Hardcoded published status

All queries now use proper parameter binding via prepared statements.
Next: Convert remaining 15+ safe hardcoded queries for consistency.

driver_training.php

@@ -1,15 +1,17 @@
-<?php
-$headerStyle = 'light';
+<?php
+$headerStyle = 'light';
 include_once('header.php');
 checkUserSession();
 
 // SQL query to fetch dates for driver training
-$sql = "SELECT course_id, date 
+$stmt = $conn->prepare("SELECT course_id, date 
         FROM courses 
-        WHERE course_type = 'driver_training' 
-        AND date >= CURDATE()";
-
-$result = $conn->query($sql);
+        WHERE course_type = ? 
+        AND date >= CURDATE()");
+$course_type = 'driver_training';
+$stmt->bind_param("s", $course_type);
+$stmt->execute();
+$result = $stmt->get_result();
 $page_id = 'driver_training';
 
 ?>
@@ -24,10 +26,10 @@ $page_id = 'driver_training';
         padding: 8px;
         font-size: 16px;
     }
-</style><?php
-    $pageTitle = 'Driver Training';
-    $breadcrumbs = [['Home' => 'index.php']];
-    require_once('components/banner.php');
+</style><?php
+    $pageTitle = 'Driver Training';
+    $breadcrumbs = [['Home' => 'index.php']];
+    require_once('components/banner.php');
 ?>
 
 <!-- Product Details Start -->