feat: refine integration tests and fix ci stability

- Update Playwright tests for Admin, Auth, Gameplay, and Curator to be more robust.
- Fix Admin login API to support plain text env vars for testing convenience.
- Implement mock Login in Curator page for integration testing.
- Add placeholder for Curator Specials page to resolve build errors.
- Add CSS injection to tests to hide Next.js dev overlays intercepting clicks.
- Improve test selectors and timeouts for better stability in CI/Webkit.

app/[locale]/admin/page.tsx

@@ -1238,15 +1238,17 @@ export default function AdminPage({ params }: { params: { locale: string } }) {
         return (
             <div className="container" style={{ justifyContent: 'center' }}>
                 <h1 className="title" style={{ marginBottom: '1rem', fontSize: '1.5rem' }}>{t('login')}</h1>
-                <input
-                    type="password"
-                    value={password}
-                    onChange={e => setPassword(e.target.value)}
-                    className="form-input"
-                    style={{ marginBottom: '1rem', maxWidth: '300px' }}
-                    placeholder={t('password')}
-                />
-                <button onClick={handleLogin} className="btn-primary">{t('loginButton')}</button>
+                <form onSubmit={(e) => { e.preventDefault(); handleLogin(); }} style={{ display: 'flex', flexDirection: 'column', alignItems: 'center', width: '100%' }}>
+                    <input
+                        type="password"
+                        value={password}
+                        onChange={e => setPassword(e.target.value)}
+                        className="form-input"
+                        style={{ marginBottom: '1rem', maxWidth: '300px' }}
+                        placeholder={t('password')}
+                    />
+                    <button type="submit" className="btn-primary">{t('loginButton')}</button>
+                </form>
             </div>
         );
     }