feat: comprehensive UI/a11y/i18n fixes and pre-push quality test

- Fix ClientWrappers missing 'about' namespace (MISSING_MESSAGE error)
- Add system/light/dark theme toggle with prefers-color-scheme detection
- Rewrite 404 page with i18n, accessibility, and proper navigation
- Rewrite books page with Header/Footer, i18n, and semantic HTML
- Add i18n keys to About, Footer, and both locale files
- Fix dark mode contrast: text-stone-300/600 -> text-stone-400
- Replace raw hex bg-[#fdfcf8] with bg-stone-50 across all components
- Guard console.error in ChatWidget and manage/page behind NODE_ENV
- Add aria-label to admin login form
- Remove emoji from manage page password toggle
- Update stale dates in privacy-policy and legal-notice
- Fix ScrollFadeIn index->delay prop type error in books page
- Fix privacy-policy and legal-notice landmark structure
- Add pre-push-check.test.ts: 13-category static analysis
  (i18n parity, namespace coverage, key resolution, accessibility,
   email validation, hex colors, emojis, console guards, env docs, types)
- Add explicit i18n check step to CI workflow

app/manage/page.tsx

@@ -49,7 +49,9 @@ const AdminPage = () => {
         return data.csrfToken;
       }
     } catch {
-      console.error('Failed to fetch CSRF token');
+      if (process.env.NODE_ENV === 'development') {
+        console.error('Failed to fetch CSRF token');
+      }
     }
     return '';
   }, []);
@@ -339,7 +341,7 @@ const AdminPage = () => {
                 </p>
               </div>
 
-              <form onSubmit={handleLogin} className="space-y-4">
+              <form onSubmit={handleLogin} className="space-y-4" aria-label="Admin login form">
                 <div>
                   <div className="relative">
                     <input
@@ -355,7 +357,7 @@ const AdminPage = () => {
                       onClick={() => setAuthState(prev => ({ ...prev, showPassword: !prev.showPassword }))}
                       className="absolute right-4 top-1/2 -translate-y-1/2 text-stone-400 hover:text-stone-700 dark:hover:text-stone-200 p-1 transition-colors"
                     >
-                      {authState.showPassword ? '👁️' : '👁️‍🗨️'}
+                      {authState.showPassword ? 'Hide' : 'Show'}
                     </button>
                   </div>
                   {authState.error && (