Add LHB Engineering case study with reusable header/footer partials and scrollable hero screenshots

includes/header.php

@@ -17,7 +17,12 @@
 
     <?php $current = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH); ?>
     <nav class="nav">
-        <a href="/" class="nav-logo">OU</a>
+        <div class="nav-left">
+            <a href="/" class="nav-logo">OU</a>
+            <?php if (str_starts_with($current, '/portfolio/')): ?>
+                <a href="/portfolio" class="nav-back">←(back)</a>
+            <?php endif; ?>
+        </div>
         <div class="nav-links">
             <a href="/#about">About</a>
             <a href="/#services">Services</a>