feat: add admin dark mode and SEO/robots.txt settings

Admin Dark Mode:
- Add AdminDarkModeContext with light/dark/system preference
- Update all admin components with Tailwind dark: classes
- Add dark mode toggle in admin header
- Persist preference in localStorage

SEO Settings:
- Add robots.txt configuration in Settings > SEO tab
- Block AI crawlers (GPTBot, ChatGPT-User, etc.) with toggle
- Custom robots.txt rules management
- Add RobotsMetaTags component for gallery pages
- Backend service for dynamic robots.txt generation
- Database migration for SEO settings storage

UI/UX Improvements:
- Consistent dark mode styling across all admin pages
- Update gallery components with themed CSS classes
- Fix input, card, and button styling for dark mode

frontend/src/components/common/Input.tsx

@@ -30,7 +30,7 @@ export const Input = React.forwardRef<HTMLInputElement, InputProps>(
         {label && (
           <label
             htmlFor={inputId}
-            className="block text-sm font-medium text-neutral-700 mb-1.5"
+            className="block text-sm font-medium text-neutral-700 dark:text-neutral-300 mb-1.5"
           >
             {label}
           </label>
@@ -38,7 +38,7 @@ export const Input = React.forwardRef<HTMLInputElement, InputProps>(
         <div className="relative">
           {leftIcon && (
             <div className="absolute inset-y-0 left-0 pl-3 flex items-center pointer-events-none">
-              <span className="text-neutral-500">{leftIcon}</span>
+              <span className="text-neutral-500 dark:text-neutral-400">{leftIcon}</span>
             </div>
           )}
           <input
@@ -59,17 +59,17 @@ export const Input = React.forwardRef<HTMLInputElement, InputProps>(
           />
           {rightIcon && (
             <div className="absolute inset-y-0 right-0 pr-3 flex items-center">
-              <span className="text-neutral-500">{rightIcon}</span>
+              <span className="text-neutral-500 dark:text-neutral-400">{rightIcon}</span>
             </div>
           )}
         </div>
         {error && (
-          <p id={`${inputId}-error`} className="mt-1.5 text-sm text-red-600">
+          <p id={`${inputId}-error`} className="mt-1.5 text-sm text-red-600 dark:text-red-400">
             {error}
           </p>
         )}
         {helperText && !error && (
-          <p id={`${inputId}-helper`} className="mt-1.5 text-sm text-neutral-500">
+          <p id={`${inputId}-helper`} className="mt-1.5 text-sm text-neutral-500 dark:text-neutral-400">
             {helperText}
           </p>
         )}

frontend/src/components/common/LanguageSelector.tsx

@@ -41,7 +41,7 @@ export const LanguageSelector: React.FC = () => {
     <div className="relative">
       <button
         onClick={() => setIsOpen(!isOpen)}
-        className="flex items-center gap-2 px-3 py-2 text-sm font-medium text-neutral-700 bg-white border border-neutral-300 rounded-lg hover:bg-neutral-50 focus:outline-none focus:ring-2 focus:ring-primary-500"
+        className="flex items-center gap-2 px-3 py-2 text-sm font-medium text-neutral-700 dark:text-neutral-200 bg-white dark:bg-neutral-800 border border-neutral-300 dark:border-neutral-600 rounded-lg hover:bg-neutral-50 dark:hover:bg-neutral-700 focus:outline-none focus:ring-2 focus:ring-primary-500"
       >
         <Globe className="w-4 h-4" />
         <currentLanguage.Flag className="w-5 h-5" />
@@ -49,15 +49,15 @@ export const LanguageSelector: React.FC = () => {
       </button>
 
       {isOpen && (
-        <div className="absolute right-0 mt-2 w-48 bg-white rounded-lg shadow-lg border border-neutral-200 py-1 z-50">
+        <div className="absolute right-0 mt-2 w-48 bg-white dark:bg-neutral-800 rounded-lg shadow-lg border border-neutral-200 dark:border-neutral-700 py-1 z-50">
           {languages.map((language) => (
             <button
               key={language.code}
               onClick={() => handleLanguageChange(language.code)}
-              className={`w-full text-left px-4 py-2 text-sm hover:bg-neutral-50 flex items-center gap-3 ${
+              className={`w-full text-left px-4 py-2 text-sm hover:bg-neutral-50 dark:hover:bg-neutral-700 flex items-center gap-3 ${
                 language.code === i18n.language
-                  ? 'text-primary-600 bg-primary-50'
-                  : 'text-neutral-700'
+                  ? 'text-primary-600 dark:text-primary-400 bg-primary-50 dark:bg-primary-900/30'
+                  : 'text-neutral-700 dark:text-neutral-300'
               }`}
             >
               <language.Flag className="w-5 h-5" />

frontend/src/components/common/RobotsMetaTags.tsx

@@ -0,0 +1,52 @@
+import { useEffect } from 'react';
+import { useQuery } from '@tanstack/react-query';
+import { getApiBaseUrl } from '../../utils/url';
+
+export const RobotsMetaTags: React.FC = () => {
+  const { data: settings } = useQuery({
+    queryKey: ['public-settings'],
+    queryFn: async () => {
+      try {
+        const response = await fetch(`${getApiBaseUrl()}/public/settings`);
+        if (response.ok) {
+          return response.json();
+        }
+        return null;
+      } catch {
+        return null;
+      }
+    },
+    staleTime: 5 * 60 * 1000,
+  });
+
+  useEffect(() => {
+    // Remove any existing robots meta tags we previously injected
+    document.querySelectorAll('meta[name="robots"][data-picpeak]').forEach(el => el.remove());
+
+    const directives: string[] = [];
+    if (settings?.seo_meta_noindex) directives.push('noindex');
+    if (settings?.seo_meta_nofollow) directives.push('nofollow');
+
+    if (directives.length > 0) {
+      const meta = document.createElement('meta');
+      meta.name = 'robots';
+      meta.content = directives.join(', ');
+      meta.setAttribute('data-picpeak', 'true');
+      document.head.appendChild(meta);
+    }
+
+    if (settings?.seo_meta_noai) {
+      const metaAi = document.createElement('meta');
+      metaAi.name = 'robots';
+      metaAi.content = 'noai, noimageai';
+      metaAi.setAttribute('data-picpeak', 'true');
+      document.head.appendChild(metaAi);
+    }
+
+    return () => {
+      document.querySelectorAll('meta[name="robots"][data-picpeak]').forEach(el => el.remove());
+    };
+  }, [settings?.seo_meta_noindex, settings?.seo_meta_nofollow, settings?.seo_meta_noai]);
+
+  return null;
+};

frontend/src/components/common/index.ts

@@ -14,6 +14,7 @@ export {
 export { OfflineIndicator, useOnlineStatus } from './OfflineIndicator';
 export { SkipLink } from './SkipLink';
 export { DynamicFavicon } from './DynamicFavicon';
+export { RobotsMetaTags } from './RobotsMetaTags';
 export { LanguageSelector } from './LanguageSelector';
 export { AuthenticatedImage } from './AuthenticatedImage';
 export { AuthenticatedVideo } from './AuthenticatedVideo';