feat: add release notes overlay with Markdown rendering

- Replace truncated plaintext release notes with full-screen overlay
  rendered via `marked` library
- Server reconnection does a hard page reload instead of custom event

server/src/wled_controller/static/js/features/update.ts

@@ -36,6 +36,7 @@ interface UpdateStatus {
 }
 
 let _lastStatus: UpdateStatus | null = null;
+let _releaseNotesBody = '';
 
 // ─── Version badge highlight ────────────────────────────────
 
@@ -383,18 +384,33 @@ function _renderUpdatePanel(status: UpdateStatus): void {
         progressBar.parentElement!.style.display = show ? '' : 'none';
     }
 
-    // Release notes preview
-    const notesEl = document.getElementById('update-release-notes');
-    if (notesEl) {
+    // Release notes button visibility
+    const notesGroup = document.getElementById('update-release-notes-group');
+    if (notesGroup) {
         if (status.has_update && status.release && status.release.body) {
-            const truncated = status.release.body.length > 500
-                ? status.release.body.slice(0, 500) + '...'
-                : status.release.body;
-            notesEl.textContent = truncated;
-            notesEl.parentElement!.style.display = '';
+            _releaseNotesBody = status.release.body;
+            notesGroup.style.display = '';
         } else {
-            notesEl.textContent = '';
-            notesEl.parentElement!.style.display = 'none';
+            _releaseNotesBody = '';
+            notesGroup.style.display = 'none';
         }
     }
 }
+
+// ─── Release Notes Overlay ─────────────────────────────────
+
+export function openReleaseNotes(): void {
+    const overlay = document.getElementById('release-notes-overlay');
+    const content = document.getElementById('release-notes-content');
+    if (overlay && content) {
+        import('marked').then(({ marked }) => {
+            content.innerHTML = marked.parse(_releaseNotesBody) as string;
+            overlay.style.display = 'flex';
+        });
+    }
+}
+
+export function closeReleaseNotes(): void {
+    const overlay = document.getElementById('release-notes-overlay');
+    if (overlay) overlay.style.display = 'none';
+}