Refactor HTMX fragment architecture: DRY split into auth endpoints + shared templates

- Created templates/partials/form/_licence.php (shared HTML, no auth logic)
- Created templates/partials/form/_format-website.php (shared HTML, no auth logic)
- Created src/FragmentRenderer.php helper for clean fragment rendering
- Created public/{admin,partage}/fragments/ subdirectories
- Created thin fragment endpoint files: auth guard + data fetch + render template
- Updated all hx-post references in templates to new fragments/ paths
- Updated partage/index.php routing for new fragments subdirectory
- Kept old fragment files as thin delegates for backward compat
- Updated nginx config: added PHP handler in /partage/ location block

app/templates/partials/form/_format-website.php

@@ -0,0 +1,48 @@
+<?php
+/**
+ * _format-website.php — Shared HTMX fragment template for the Site web fieldset.
+ *
+ * Returns the website URL + label inputs when "Site web" is among the selected
+ * format checkboxes. Pure presentation — receives all data via variables.
+ *
+ * Expected variables:
+ *   string  $fieldsetId   — HTML id for the <fieldset> ('website-url-fieldset' or 'edit-website-url-fieldset')
+ *   array   $selectedFormats — selected format_type IDs
+ *   int     $websiteFormatId — ID of the "Site web" format_type
+ *   string  $websiteUrl      — current value (for repopulation)
+ *   string  $websiteLabel    — current value (for repopulation)
+ */
+
+if (!$websiteFormatId) {
+    echo '<fieldset id="' . $fieldsetId . '" style="display:none"></fieldset>';
+    return;
+}
+
+if (!in_array((int)$websiteFormatId, array_map('intval', $selectedFormats), true)) {
+    echo '<fieldset id="' . $fieldsetId . '" style="display:none"></fieldset>';
+    return;
+}
+
+$escUrl   = htmlspecialchars($websiteUrl);
+$escLabel = htmlspecialchars($websiteLabel);
+?>
+<fieldset id="<?= $fieldsetId ?>">
+    <legend>Site web</legend>
+    <div class="admin-form-group">
+        <label for="website_url">URL du site :</label>
+        <div class="admin-file-input">
+            <input type="url" id="website_url" name="website_url"
+                   value="<?= $escUrl ?>"
+                   placeholder="https://mon-tfe.erg.be">
+            <small>Si le TFE est un site web, entrez son URL ici. Il sera affiché comme un site embarqué sur la page du TFE.</small>
+        </div>
+    </div>
+    <div class="admin-form-group">
+        <label for="website_label">Légende :</label>
+        <input type="text" id="website_label" name="website_label"
+               value="<?= $escLabel ?>"
+               placeholder="Description du site (optionnel)"
+               class="admin-file-label-input"
+               style="max-width:400px;">
+    </div>
+</fieldset>