fix: перевести SEO-теги и document lang на английский

frontend/index.html

@@ -1,11 +1,35 @@
 <!doctype html>
-<html lang="ru">
+<html lang="en">
   <head>
     <meta charset="UTF-8" />
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
     <meta name="theme-color" content="#0b0b0b" />
-    <title>Aurum — Личные финансы</title>
+    <title>Aurum — Personal Finance</title>
+    <meta
+      name="description"
+      content="Aurum is a self-hosted personal finance operating system: cash flow, net worth, budgets, subscriptions, assets, and every income stream in one place."
+    />
+    <meta
+      name="keywords"
+      content="personal finance, finance tracker, budgeting, self-hosted, cash flow, net worth, expense tracker, subscription tracker, crypto tracker, family budget"
+    />
+    <meta name="author" content="Aurum" />
+    <!-- Self-hosted app without a fixed public domain, so og:url/og:image
+         are left out — each deployment would need its own values. -->
+    <meta property="og:title" content="Aurum — Personal Finance" />
+    <meta
+      property="og:description"
+      content="A self-hosted personal finance operating system: cash flow, net worth, budgets, subscriptions, and assets."
+    />
+    <meta property="og:type" content="website" />
+    <meta property="og:locale" content="en_US" />
+    <meta name="twitter:card" content="summary" />
+    <meta name="twitter:title" content="Aurum — Personal Finance" />
+    <meta
+      name="twitter:description"
+      content="A self-hosted personal finance operating system: cash flow, net worth, budgets, subscriptions, and assets."
+    />
     <!-- Runs before the first paint to avoid a wrong-theme flash. Kept in its
          own file (public/theme-init.js), not inline, so the CSP in
          frontend/nginx.conf can forbid inline scripts entirely. -->