Desktop: Help icon update red dot should track Desktop updater, not core release notes

On Desktop (Electron), the help icon red dot currently indicates core (ComfyUI) release notes are newer than backend `/system_stats.system.comfyui_version`, which incorrectly pegs Desktop UX to core updates.

Current:
- `src/components/sidebar/SidebarHelpCenterIcon.vue` uses `useReleaseStore().shouldShowRedDot` for the badge.
- `src/platform/updates/common/releaseStore.ts` fetches `GET https://api.comfy.org/releases?project=comfyui...` and compares vs backend `comfyui_version`.

Expected:
- On Electron, the help icon “update” red dot reflects Desktop app update availability (todestkop autoUpdater rail), not core release notes.
- Automatic background checking for the dot should be gated by `Comfy-Desktop.AutoUpdate`.
- Conflict red dot behavior remains unchanged.

Notes:
- Desktop updater APIs exist: `electronAPI.checkForUpdates()` / `electronAPI.restartAndInstall()` (see `src/extensions/core/electronAdapter.ts`).

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-7544-Desktop-Help-icon-update-red-dot-should-track-Desktop-updater-not-core-release-notes-2cb6d73d365081dd8487f5bcaf18a43f) by [Unito](https://www.unito.io)