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/components/ActivityFeed.tsx

@@ -134,7 +134,7 @@ export default function ActivityFeed({
               transition={{ duration: 0.5 }}
               className="space-y-4"
             >
-              <p className="text-base sm:text-lg md:text-xl lg:text-2xl font-light leading-tight text-stone-300 italic">
+              <p className="text-base sm:text-lg md:text-xl lg:text-2xl font-light leading-tight text-stone-400 dark:text-stone-400 italic">
                 &ldquo;{allQuotes[quoteIndex].content}&rdquo;
               </p>
               <p className="text-xs font-black text-stone-400 dark:text-stone-500 uppercase tracking-widest">
@@ -143,7 +143,7 @@ export default function ActivityFeed({
             </motion.div>
           </AnimatePresence>
         </div>
-        <div className="flex items-center gap-2 text-[10px] font-black uppercase tracking-widest text-stone-400 dark:text-stone-600 pt-4 border-t border-stone-100 dark:border-stone-800">
+        <div className="flex items-center gap-2 text-[10px] font-black uppercase tracking-widest text-stone-400 dark:text-stone-400 pt-4 border-t border-stone-100 dark:border-stone-800">
           <span className="w-1.5 h-1.5 rounded-full bg-stone-200 dark:bg-stone-700 animate-pulse" /> 
           {t("idleStatus")}
         </div>
@@ -160,7 +160,7 @@ export default function ActivityFeed({
             <span className="text-[10px] font-black uppercase tracking-widest text-emerald-600 dark:text-emerald-400">{t("codingNow")}</span>
           </div>
           <p className="font-bold text-stone-900 dark:text-white text-lg truncate">{data.coding.project}</p>
-          <p className="text-xs text-stone-500 dark:text-white/50 truncate">{data.coding.file}</p>
+          <p className="text-xs text-stone-500 dark:text-stone-400 truncate">{data.coding.file}</p>
         </motion.div>
       )}
 
@@ -236,7 +236,7 @@ export default function ActivityFeed({
             </div>
             <div className="min-w-0 flex flex-col justify-center">
               <p className="font-bold text-[#1DB954] dark:text-[#1DB954] text-base truncate leading-tight mb-1 hover:underline">{data.music.track}</p>
-              <p className="text-sm text-stone-600 dark:text-white/60 truncate font-medium">{data.music.artist}</p>
+              <p className="text-sm text-stone-600 dark:text-stone-400 truncate font-medium">{data.music.artist}</p>
             </div>
           </a>
           {/* Subtle Spotify branding gradient */}