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.

packages/i18n/rsbuild.config.ts

@@ -0,0 +1,27 @@
+import { definePackageConfig } from '@ermnvldmr/rsbuild-config/dev';
+
+export default definePackageConfig({
+  source: {
+    entry: {
+      index: './src/index.ts',
+      dev: './src/dev.ts',
+      testing: './src/testing.ts',
+    },
+    alias: { '@': './src' },
+  },
+  output: {
+    target: 'web',
+    distPath: { root: 'dist', js: '' },
+    filename: { js: '[name].js' },
+    cleanDistPath: true,
+  },
+  tools: {
+    htmlPlugin: false,
+    rspack: {
+      output: { library: { type: 'module' } },
+      experiments: { outputModule: true },
+      externals: ['react', 'react/jsx-runtime', 'react/jsx-dev-runtime'],
+      externalsType: 'module',
+    },
+  },
+});