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/vite-env.d.ts

@@ -1,2 +1,13 @@
 /// <reference types="vite/client" />
 /// <reference types="vitest" />
+
+// Swiper CSS module declarations
+declare module 'swiper/css' {
+  const content: string;
+  export default content;
+}
+
+declare module 'swiper/css/free-mode' {
+  const content: string;
+  export default content;
+}