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/ChatWidget.tsx

@@ -196,11 +196,13 @@ export default function ChatWidget() {
 
       if (!response.ok) {
         const errorText = await response.text().catch(() => "Unknown error");
-        console.error("Chat API error:", {
-          status: response.status,
-          statusText: response.statusText,
-          error: errorText,
-        });
+        if (process.env.NODE_ENV === 'development') {
+          console.error("Chat API error:", {
+            status: response.status,
+            statusText: response.statusText,
+            error: errorText,
+          });
+        }
         throw new Error(
           `Failed to get response: ${response.status} - ${errorText.substring(0, 100)}`,
         );
@@ -229,7 +231,9 @@ export default function ChatWidget() {
 
       setMessages((prev) => [...prev, botMessage]);
     } catch (error) {
-      console.error("Chat error:", error);
+      if (process.env.NODE_ENV === 'development') {
+        console.error("Chat error:", error);
+      }
 
       const errorMessage: Message = {
         id: (Date.now() + 1).toString(),
@@ -436,7 +440,7 @@ export default function ChatWidget() {
             </div>
 
             {/* Input */}
-            <div className="p-4 bg-[#fdfcf8] border-t border-[#e7e5e4]">
+            <div className="p-4 bg-stone-50 border-t border-[#e7e5e4]">
               <div className="flex gap-2">
                 <input
                   ref={inputRef}
@@ -446,7 +450,7 @@ export default function ChatWidget() {
                   onKeyPress={handleKeyPress}
                   placeholder="Ask anything..."
                   disabled={isLoading}
-                  className="flex-1 px-4 py-3 text-sm bg-[#f5f5f4] text-[#292524] rounded-xl border border-[#e7e5e4] focus:outline-none focus:ring-2 focus:ring-[#e7e5e4] focus:border-[#a8a29e] focus:bg-[#fdfcf8] disabled:opacity-50 disabled:cursor-not-allowed placeholder:text-[#78716c] transition-all shadow-inner"
+                  className="flex-1 px-4 py-3 text-sm bg-[#f5f5f4] text-[#292524] rounded-xl border border-[#e7e5e4] focus:outline-none focus:ring-2 focus:ring-[#e7e5e4] focus:border-[#a8a29e] focus:bg-stone-50 disabled:opacity-50 disabled:cursor-not-allowed placeholder:text-[#78716c] transition-all shadow-inner"
                 />
                 <button
                   onClick={handleSend}