feat(admin-ui): softer pre-material styling and dark theme

- Rebuild admin console styling on semantic CSS variables (light + dark palettes)
- Soften palette, shadows and corner radii for a calmer pre-material look
- Add theme provider with light/dark toggle in the topbar and login header
- Respect prefers-color-scheme and persist choice, with anti-FOUC inline script
- Polish Russian translations (yo letters, consistent 'Звёзды' currency, wording)
- Rebuild dist bundle to match the updated source

cmd/telesrv-admin/web/src/main.tsx

@@ -2,12 +2,15 @@ import React from "react";
 import ReactDOM from "react-dom/client";
 import { App } from "./App";
 import { I18nProvider } from "./i18n";
+import { ThemeProvider } from "./theme";
 import "./styles.css";
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>
-    <I18nProvider>
-      <App />
-    </I18nProvider>
+    <ThemeProvider>
+      <I18nProvider>
+        <App />
+      </I18nProvider>
+    </ThemeProvider>
   </React.StrictMode>
 );