Both Dashboard and Lite have "Check for Updates" links in their About dialogs, but they just open the GitHub releases page in the browser.

Add actual update checking that hits the GitHub API (/releases/latest) to compare the running version against the latest release:

• Automatic check on startup (once per 24 hours, configurable)
• On-demand check via the About dialog link
• Show notification when a new version is available with link to download
• Never crash if GitHub is unreachable

Applies to both Dashboard and Lite editions.