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/app.ts

@@ -203,6 +203,7 @@ import {
     loadUpdateStatus, initUpdateListener, checkForUpdates,
     loadUpdateSettings, saveUpdateSettings, dismissUpdate,
     initUpdateSettingsPanel, applyUpdate,
+    openReleaseNotes, closeReleaseNotes,
 } from './features/update.ts';
 
 // ─── Register all HTML onclick / onchange / onfocus globals ───
@@ -572,6 +573,8 @@ Object.assign(window, {
     dismissUpdate,
     initUpdateSettingsPanel,
     applyUpdate,
+    openReleaseNotes,
+    closeReleaseNotes,
 
     // appearance
     applyStylePreset,