Various build shenenigans (#5)

This PR extends the build pipeline of the www service to support
locale-prefixed static builds (EN/RU) with build-time SSG output
injection, while also refactoring UI typography to a tokenized Tailwind
v4 @theme-driven approach.

Changes:

- Add build-time SSG plugin to @ermnvldmr/rsbuild-config and wire
multi-locale builds (/en/, /ru/) into services/www.
- Introduce new @ermnvldmr/i18n package (locale constants, path helpers,
keysets, pluralization) and apply it to www navigation/text.
- Refactor ui typography to a shared getTypographyClassNames utility +
Tailwind token definitions, with stl/cn updated for correct
Tailwind-merge behavior.

services/www/content/registry.ts

@@ -1,7 +1,7 @@
 import React from 'react';
-import * as TestArticle from './articles/2026/test-article.mdx';
-import * as MatrixServerDeploymentGuide from './articles/2026/matrix-server-deployment-guide.mdx';
-import * as XrayCoreSubnetMimicry from './articles/2026/xray-core-subnet-mimicry.mdx';
+import * as TestArticle from './articles/2026/test-article.en.mdx';
+import * as MatrixServerDeploymentGuide from './articles/2026/matrix-server-deployment-guide.en.mdx';
+import * as XrayCoreSubnetMimicry from './articles/2026/xray-core-subnet-mimicry.en.mdx';
 
 export interface Article {
   slug: string;