feat: revamp dashboard, trades, and add landing/legal pages

- Major UI updates across dashboard, analytics, posts, trades, settings
- New landing page, robots/sitemap, contact/privacy/terms pages
- Updated globals.css with extensive styling and new landing.css
- Refactor signedRequest, realtime data hook, and dashboard store

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

i18n.ts

@@ -1,6 +1,9 @@
 import { getRequestConfig } from 'next-intl/server'
 
-export const locales = ['en', 'ar', 'pt-BR', 'zh', 'ja'] as const
+// English-only. Other locales were listed historically but have no message
+// files, which caused browsers with non-English Accept-Language to be routed
+// to a missing bundle. Keep in sync with messages/*.json.
+export const locales = ['en'] as const
 export type Locale = (typeof locales)[number]
 export const defaultLocale: Locale = 'en'