fix(settings): keep Steam ID as string and store the new token

Number("76561198005679788") is 76561198005679790 in JavaScript, so the wrong
Steam ID was saved. The Steam ID now stays a 17-digit string. Theme and
language saves no longer send steamId 0. After a save the new token from Auth
replaces the old one.

Add Vitest and run it in CI.

.gitea/workflows/docker-publish.yml

@@ -29,6 +29,9 @@ jobs:
       - name: Lint & Type Check
         run: npm run lint --if-present
 
+      - name: Unit Tests
+        run: npm test
+
       # Build the Vite React application
       - name: Build Production
         run: npm run build