feat(i18n): Integrate next-intl, localize core UI, add regional locales and zh-TW Discover sources

**Overview**
- Integrates next-intl (App Router, no i18n routing) with cookie-based locale and Accept-Language fallback.
- Adds message bundles and regional variants; sets en-US as the default.

**Key changes**
- i18n foundation
  - Adds request-scoped config to load messages per locale and injects NextIntlClientProvider in [layout.tsx]
  - Adds/updates messages for: en-US, en-GB, zh-TW, zh-HK, zh-CN, ja, ko, fr-FR, fr-CA, de.
Centralizes LOCALES, LOCALE_LABELS, and DEFAULT_LOCALE in [locales.ts]
  - Adds LocaleSwitcher (cookie-based) and [LocaleBootstrap]

- Pages and components
  - Localizes Sidebar, Home (including metadata/manifest), Settings, Discover, Library.
  - Localizes common components: MessageInput, Attach, Focus, Optimization, MessageBox, MessageSources, SearchImages, SearchVideos, EmptyChat, NewsArticleWidget, WeatherWidget.

- APIs
  - Weather API returns localized condition strings server-side.

- UX and quality
  - Converts all remaining <img> to Next Image.
  - Updates browserslist/caniuse DB to silence warnings.
  - Security: Settings API Key inputs are now password fields and placeholders were removed.

src/components/MessageInputActions/Optimization.tsx

@@ -7,24 +7,19 @@ import {
   Transition,
 } from '@headlessui/react';
 import { Fragment } from 'react';
+import { useTranslations } from 'next-intl';
 
 const OptimizationModes = [
   {
     key: 'speed',
-    title: 'Speed',
-    description: 'Prioritize speed and get the quickest possible answer.',
     icon: <Zap size={20} className="text-[#FF9800]" />,
   },
   {
     key: 'balanced',
-    title: 'Balanced',
-    description: 'Find the right balance between speed and accuracy',
     icon: <Sliders size={20} className="text-[#4CAF50]" />,
   },
   {
     key: 'quality',
-    title: 'Quality (Soon)',
-    description: 'Get the most thorough and accurate answer',
     icon: (
       <Star
         size={16}
@@ -41,6 +36,7 @@ const Optimization = ({
   optimizationMode: string;
   setOptimizationMode: (mode: string) => void;
 }) => {
+  const t = useTranslations('components.optimization');
   return (
     <Popover className="relative w-full max-w-[15rem] md:max-w-md lg:max-w-lg">
       <PopoverButton
@@ -53,10 +49,7 @@ const Optimization = ({
               ?.icon
           }
           <p className="text-xs font-medium">
-            {
-              OptimizationModes.find((mode) => mode.key === optimizationMode)
-                ?.title
-            }
+            {t(`modes.${optimizationMode}.title`)}
           </p>
           <ChevronDown size={20} />
         </div>
@@ -87,10 +80,12 @@ const Optimization = ({
               >
                 <div className="flex flex-row items-center space-x-1 text-black dark:text-white">
                   {mode.icon}
-                  <p className="text-sm font-medium">{mode.title}</p>
+                  <p className="text-sm font-medium">
+                    {t(`modes.${mode.key}.title`)}
+                  </p>
                 </div>
                 <p className="text-black/70 dark:text-white/70 text-xs">
-                  {mode.description}
+                  {t(`modes.${mode.key}.description`)}
                 </p>
               </PopoverButton>
             ))}