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

public/assets/css/editor.css

@@ -0,0 +1,52 @@
+.CodeMirror {
+    height: auto;
+    min-height: 500px;
+    border: 1px solid #dee2e6;
+    border-radius: 0.25rem;
+    font-size: 0.9rem;
+    font-family: ui-monospace, SFMono-Regular, 'SF Mono', Menlo, Consolas, monospace;
+}
+
+.CodeMirror-scroll {
+    min-height: 500px;
+}
+
+.editor-toolbar {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 0.125rem;
+    padding: 0.375rem 0.5rem;
+    background: #f8f9fa;
+    border: 1px solid #dee2e6;
+    border-bottom: none;
+    border-radius: 0.25rem 0.25rem 0 0;
+}
+
+.editor-toolbar .vr {
+    height: 22px;
+    opacity: 0.3;
+}
+
+.editor-toolbar .btn {
+    line-height: 1;
+}
+
+.editor-wrapper {
+    border-radius: 0 0 0.25rem 0.25rem;
+    overflow: hidden;
+}
+
+.editor-wrapper .CodeMirror {
+    border-top: none;
+    border-radius: 0;
+}
+
+.card-media-item {
+    transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
+    border: 1px solid #dee2e6;
+}
+.card-media-item:hover {
+    border-color: #0d6efd;
+    box-shadow: 0 0 0 0.2rem rgba(13, 110, 253, 0.15);
+}