feat: single entry point routing — convert to front controller pattern

- Create app/public/index.php as front controller (bootstrap + Dispatcher)
- Rewrite app/router.php for PHP dev server → all non-asset requests to index.php
- Update Dispatcher to render full page layouts (head+header+view+footer)
- Move public view templates into templates/public/ (home, search, tfe, about, repertoire)
- Delete dead direct-access public/*.php files (apropos, search, tfe, licence, repertoire)
- Add clean URL routes to Dispatcher (/search, /tfe, /repertoire, /apropos, /licence, /media)
- Remove .php extensions from all internal links (header, views, templates, URLs)
- Update OG tags in controllers to use clean URLs
- Update nginx posterg.conf → front-controller try_files pattern, block direct .php access
- Update header.php and search-bar.php form actions to clean URLs
- Switch AboutController nav key from 'nav' to 'currentNav' for consistency

app/templates/header.php

@@ -35,21 +35,21 @@ $_thesisId     = $_GET['id'] ?? null;
 
     <nav aria-label="Navigation principale">
         <div class="nav-left">
-            <a href="/index.php" class="nav-logo">Xamxam</a>
+            <a href="/" class="nav-logo">Xamxam</a>
             <ul class="nav-left-links">
                 <li>
-                    <a href="/repertoire.php"
+                    <a href="/repertoire"
                        <?= ($_navCurrent === 'repertoire') ? 'aria-current="page"' : '' ?>>Répertoire</a>
                 </li>
             </ul>
         </div>
         <ul class="nav-right-links">
             <li>
-                <a href="/licence.php"
+                <a href="/licence"
                    <?= ($_navCurrent === 'licence') ? 'aria-current="page"' : '' ?>>Licences</a>
             </li>
             <li>
-                <a href="/apropos.php"
+                <a href="/apropos"
                    <?= ($_navCurrent === 'apropos') ? 'aria-current="page"' : '' ?>>À Propos</a>
             </li>
         </ul>
@@ -65,7 +65,7 @@ $_thesisId     = $_GET['id'] ?? null;
 $searchBarValue = $searchBarValue ?? $_GET['query'] ?? '';
 ?>
 <div class="header-search-wrap">
-    <form method="GET" action="/search.php"
+    <form method="GET" action="/search"
           role="search" aria-label="Recherche">
         <label for="site-search-input" class="sr-only">Recherche</label>
         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"