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/locales/en.json

@@ -1931,6 +1931,7 @@
     "update.last_check": "Last check",
     "update.never": "never",
     "update.release_notes": "Release Notes",
+    "update.view_release_notes": "View Release Notes",
     "update.auto_check_label": "Auto-Check Settings",
     "update.auto_check_hint": "Periodically check for new releases in the background.",
     "update.enable": "Enable auto-check",