Adds self-hosted update system

Implements a self-hosted update mechanism, allowing the application to be updated from a corporate network share without relying on third-party services.

This includes:
- Functionality to check for updates
- Download installers
- Verify checksums
- Install updates with UAC elevation

Configuration is managed via the config.ini file, with automatic checks on startup. A new settings UI is also included.

frontend/src/lib/components/MailViewer.svelte

@@ -115,10 +115,6 @@
           mailState.currentEmail.body = processedBody;
         }
       }
-
-      if (dev) {
-        console.debug('emailObj:', mailState.currentEmail);
-      }
       console.info('Current email changed:', mailState.currentEmail?.subject);
 
       if (mailState.currentEmail !== null) {