Refactor apropos/charte/licence pages: shared layout, TOC anchors, and UI polish

Unify the three public pages (à propos, charte, licence) onto a single
grid layout (.page-content) with sticky TOC sidebar, replacing the old
separate  /  /  markup.

- Merge about.php, charte.php, licence.php templates into shared
  .page-content / .content-section structure
- Add CommonMark HeadingPermalinkExtension for stable heading anchors
- Use SlugNormalizer for TOC links so they match rendered heading IDs
- Standardize link styling across content blocks: bold black, accent on
  hover (consistent with global link style)
- Fix code block wrapping: use pre-wrap instead of pre, constrain grid
  columns with min-width:0, auto scrollbar
- Fix apropos page grid placement: force content-section into column 2
  so contacts and credits stay in the content area, not the sidebar

Also includes accumulated WIP changes:
- Header gradient: hardcoded purple-to-green (replaces CSS variables)
- Search placeholder font
- Duration field: replace minutes/sec/heures with h:m:s time inputs
- TFE file optional for formats 1,4,6 with client-side JS toggle
- Licence form: em-dash to hyphen, details/summary classes
- Pill search: block Enter key form submission when no results
- Draft autosave: remove CSRF rotation (broke concurrent FilePond uploads)
- Language pill: clear hints for excluded main languages
- Search results: gradient placeholder cards for items without covers
- TFE display: format durée values as XhYm instead of decimal

app/templates/public/charte.php

@@ -1,30 +1,23 @@
-<main class="apropos-main" id="main-content">
-    <div class="apropos-layout">
+<main class="page-content" id="main-content">
 
-        <!-- LEFT: sticky table of contents -->
-        <?php if (!empty($tocItems)): ?>
-        <nav class="apropos-toc" aria-label="Sections de la page">
-            <p class="apropos-toc-label">Parties</p>
-            <ul>
-                <?php foreach ($tocItems as $item): ?>
-                <li><a href="<?= htmlspecialchars($item['href']) ?>"><?= htmlspecialchars($item['label']) ?></a></li>
-                <?php endforeach; ?>
-            </ul>
-        </nav>
+    <!-- LEFT: sticky table of contents -->
+    <?php if (!empty($tocItems)): ?>
+    <nav class="apropos-toc" aria-label="Sections de la page">
+        <p class="apropos-toc-label">PARTIES</p>
+        <ul>
+            <?php foreach ($tocItems as $item): ?>
+            <li><a href="<?= htmlspecialchars($item['href']) ?>"><?= htmlspecialchars($item['label']) ?></a></li>
+            <?php endforeach; ?>
+        </ul>
+    </nav>
+    <?php endif; ?>
+
+    <div class="content">
+        <?php if (!empty(trim($content))): ?>
+            <?= $html ?>
+        <?php else: ?>
+            <p>Contenu à venir.</p>
         <?php endif; ?>
-
-        <!-- MIDDLE: main prose -->
-        <div class="apropos-content">
-            <section class="apropos-section">
-                <div class="prose">
-                    <?php if (!empty(trim($content))): ?>
-                        <?= $html ?>
-                    <?php else: ?>
-                        <p>Contenu à venir.</p>
-                    <?php endif; ?>
-                </div>
-            </section>
-        </div>
-
     </div>
+
 </main>