feat: rename memoire to tfe and improve styling

- Rename memoire.php to tfe.php throughout codebase
- Create dedicated tfe.css with rounded header/main/footer layout
- Move metadata (orientation, AP program, finality, keywords) to header
- Move back button from header to footer
- Create shared templates/head.php for common HTML head section
- Maintain rounded borders (40px) matching main site design
- Keep purple header (#9557b5), green main (#3c856b), dark footer (#222)
- Improve content readability with centered max-width layout
- Add responsive design for mobile devices

public/index.php

@@ -44,7 +44,7 @@ include APP_ROOT . '/templates/header.php';
 
 <main>
     <?php foreach ($itemsToLoad as $item): ?>
-        <a href="memoire.php?id=<?= (int)$item["id"] ?>" class="card-link">
+        <a href="tfe.php?id=<?= (int)$item["id"] ?>" class="card-link">
             <div class="card">
                 <div class="card-content">
                     <h2 class="title"><?= htmlspecialchars($item["title"]) ?></h2>