add form help blocks: DB table, admin editor, live rendering in partage form

app/templates/admin/contenus.php

@@ -2,14 +2,13 @@
     <h1>Contenus</h1>
 
     <?php
-    $flashSuccess = App::consumeFlash('success');
-    $flashError   = App::consumeFlash('error');
+    $flash = App::consumeFlash();
     ?>
-    <?php if ($flashSuccess): ?>
-    <div class="flash-success" role="alert"><?= htmlspecialchars($flashSuccess) ?></div>
+    <?php if ($flash['success']): ?>
+    <div class="flash-success" role="alert"><?= htmlspecialchars($flash['success']) ?></div>
     <?php endif; ?>
-    <?php if ($flashError): ?>
-    <div class="flash-error" role="alert"><?= htmlspecialchars($flashError) ?></div>
+    <?php if ($flash['error']): ?>
+    <div class="flash-error" role="alert"><?= htmlspecialchars($flash['error']) ?></div>
     <?php endif; ?>
 
     <h2>Pages statiques</h2>

app/templates/partials/form/form-help-block.php

@@ -0,0 +1,26 @@
+<?php
+/**
+ * Renders a single form help block as HTML.
+ *
+ * Variables consumed:
+ *   string $helpContent — raw Markdown string from the DB (may be empty).
+ *
+ * Outputs nothing when $helpContent is empty or whitespace-only.
+ * Parsedown must already be autoloaded (it is, via bootstrap → APP_ROOT/src/).
+ */
+
+$helpContent = trim($helpContent ?? '');
+if ($helpContent === '') {
+    return;
+}
+
+require_once APP_ROOT . '/src/Parsedown.php';
+$pd   = new Parsedown();
+$pd->setSafeMode(true);
+$html = $pd->text($helpContent);
+?>
+<div class="form-help-block">
+    <?= $html ?>
+</div>
+<?php
+unset($helpContent, $pd, $html);