feat: obfuscate all email addresses and mailto links as HTML entities

Added EmailObfuscator class (src/EmailObfuscator.php) that converts
email addresses to HTML decimal entities (e.g. foo@...)
so browsers render them correctly but bots and scrapers see gibberish.

Methods:
- email($addr): obfuscate for display in HTML content
- mailto($addr): return obfuscated mailto: href
- obfuscateHtml($html): post-process rendered HTML to obfuscate all
  mailto: links (used after Parsedown/Markdown rendering)

Applied to:
- partage/index.php: mailto link at top + error scenarios via _flash_contact
  flag rendered in form.php (outside htmlspecialchars to avoid double-escape)
- admin/acces.php: request email mailto links
- admin/file-access.php: request email mailto links
- public/about.php: contact email mailto links
- public/tfe.php: author contact mailto links
- AboutController: Parsedown output post-processing
- LicenceController: Parsedown output post-processing
- Dispatcher::render(): require_once EmailObfuscator for all public views

Also fixed _flash_contact session flag in form.php partial to show
contact email line on share link validation errors (separate from
flash_error/warning to bypass htmlspecialchars double-escaping).

app/templates/partials/form/form.php

@@ -110,10 +110,12 @@ $checkedFormatsForSiteWeb = $checkedFormatsForSiteWeb ?? [];
     $flashError = $_SESSION["_flash_error"] ?? null;
     $flashWarning = $_SESSION["_flash_warning"] ?? null;
     $flashSuccess = $_SESSION["_flash_success"] ?? null;
+    $flashContact = $_SESSION["_flash_contact"] ?? false;
     unset(
         $_SESSION["_flash_error"],
         $_SESSION["_flash_warning"],
         $_SESSION["_flash_success"],
+        $_SESSION["_flash_contact"],
     );
     ?>
     <?php if ($flashError): ?>
@@ -127,6 +129,13 @@ $checkedFormatsForSiteWeb = $checkedFormatsForSiteWeb ?? [];
     ) ?></div>
     <script>document.addEventListener('DOMContentLoaded',function(){var el=document.getElementById('flash-warning');if(el){el.scrollIntoView({behavior:'smooth',block:'center'});el.focus();}});</script>
     <?php endif; ?>
+    <?php if ($flashContact && $mode === 'partage'): ?>
+    <?php require_once APP_ROOT . '/src/EmailObfuscator.php'; ?>
+    <div class="flash-info" role="alert">
+        Si le problème persiste, envoyez un e-mail à
+        <a href="<?= EmailObfuscator::mailto('xamxam@erg.be') ?>"><?= EmailObfuscator::email('xamxam@erg.be') ?></a>.
+    </div>
+    <?php endif; ?>
     <?php if ($flashSuccess): ?>
     <div class="flash-success" role="alert"><?= htmlspecialchars(
         $flashSuccess,