Media browser: recursive scan entire content/ tree, /-media/ URL prefix, editor change detection fix

- handleMediaList() now scans content/ recursively for all media files
- URLs use /-media/ prefix mapping directly to content/ (no special cases)
- index.php: added /-media/ route, kept /-assets/ for backward compat
- editor-toolbar.js: fixed editor.on('change') placement (was inside switchMode)
- content-edit.php and content-new.php: back-btn unsaved-changes detection
- Removed unused __editorCleanup global

admin/templates/pages/content-dir-form.php

@@ -0,0 +1,26 @@
+<h2 class="mb-4"><i class="bi bi-pencil"></i> Map hernoemen</h2>
+
+<form method="post" class="card shadow-sm">
+    <input type="hidden" name="csrf_token" value="<?= htmlspecialchars($csrf) ?>">
+
+    <div class="card-body">
+        <div class="mb-3">
+            <label class="form-label text-muted">Huidige mapnaam</label>
+            <p class="form-control-plaintext fw-bold"><?= htmlspecialchars(basename($fullPath)) ?></p>
+        </div>
+        <div class="mb-3">
+            <label for="new_name" class="form-label">Nieuwe naam</label>
+            <input type="text" class="form-control" id="new_name" name="new_name"
+                   value="<?= htmlspecialchars(basename($fullPath)) ?>" required autofocus>
+            <div class="form-text">Alleen letters, cijfers, punten, underscores en streepjes.</div>
+        </div>
+        <?php if (!empty($message)): ?>
+            <div class="alert alert-<?= $messageType ?>"><?= htmlspecialchars($message) ?></div>
+        <?php endif; ?>
+    </div>
+
+    <div class="card-footer text-end">
+        <a href="admin.php?route=content&dir=<?= urlencode(dirname($dir) === '.' ? '' : dirname($dir)) ?>" class="btn btn-secondary">Annuleren</a>
+        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg"></i> Opslaan</button>
+    </div>
+</form>