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/search.php

@@ -333,7 +333,7 @@ include APP_ROOT . '/templates/header.php'; ?>
         <div class="columns is-multiline">
           <?php foreach ($results as $item): ?>
             <div class="column is-one-fifth">
-              <a href="memoire.php?id=<?= (int)$item['id']; ?>" class="card-link">
+              <a href="tfe.php?id=<?= (int)$item['id']; ?>" class="card-link">
                 <div class="card">
                   <?php
                   // Get cover image from thesis_files if available