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.

src/utils/validation.test.js

@@ -0,0 +1,30 @@
+import {describe, expect, it} from 'vitest';
+import {registrationSchema, settingsSchema} from './validation.js';
+
+const settings = (steamId) => ({useDarkTheme: true, language: 'de', steamId});
+
+describe('steamId validation', () => {
+    it('keeps a SteamID64 as the exact string', () => {
+        // Number('76561198005679788') is 76561198005679790
+        expect(settingsSchema.parse(settings('76561198005679788')).steamId).toBe('76561198005679788');
+    });
+
+    it('trims whitespace', () => {
+        expect(settingsSchema.parse(settings(' 76561198005679788 ')).steamId).toBe('76561198005679788');
+    });
+
+    it.each(['', '12345', '7656119800567978x', '765611980056797880'])('rejects %j', (steamId) => {
+        expect(settingsSchema.safeParse(settings(steamId)).success).toBe(false);
+    });
+
+    it('keeps the exact string on registration', () => {
+        const result = registrationSchema.parse({
+            email: 'a@b.de',
+            password: 'password1',
+            passwordConfirmation: 'password1',
+            inviteCode: 'code',
+            steamId: '76561198005679788',
+        });
+        expect(result.steamId).toBe('76561198005679788');
+    });
+});