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/stl/src/lib/functions/cn/cn.ts

@@ -1,5 +1,20 @@
 import { clsx, type ClassValue } from 'clsx';
-import { twMerge } from 'tailwind-merge';
+import { extendTailwindMerge } from 'tailwind-merge';
+
+const RB_TYPES = ['display', 'headline', 'title', 'body', 'label'] as const;
+const RB_SIZES = ['l', 'm', 's'] as const;
+
+const rbFontSizeClasses = RB_TYPES.flatMap((type) =>
+  RB_SIZES.map((size) => `${type}-${size}`)
+);
+
+const twMerge = extendTailwindMerge({
+  extend: {
+    classGroups: {
+      'font-size': [{ 'text-rb': rbFontSizeClasses }],
+    },
+  },
+});
 
 /**
  * Combines and merges CSS class names using clsx and tailwind-merge.
@@ -7,6 +22,10 @@ import { twMerge } from 'tailwind-merge';
  * This utility function combines the power of clsx for conditional class handling
  * with tailwind-merge for proper Tailwind CSS class deduplication and conflict resolution.
  *
+ * Tailwind-merge is configured to recognise `text-rb-{type}-{size}` classes
+ * (e.g. `text-rb-body-m`) as font-size utilities so they do not conflict with
+ * text-color classes such as `text-[var(--rb-text)]`.
+ *
  * @param inputs - Class values to combine (strings, objects, arrays, etc.)
  * @returns Merged class string with conflicts resolved
  *

packages/stl/src/lib/react/useLocalStorage/useLocalStorage.ts

@@ -39,9 +39,8 @@ export function useLocalStorage<T>(
   const getSnapshot = useCallback(() => manager.get(), [manager]);
 
   const value = useSyncExternalStore(subscribe, getSnapshot, () => {
-    // During SSR, we can't access localStorage.
-    // However, createLocalStorage is designed to throw if accessed during SSR.
-    // This hook is intended to be used in client-side components.
+    // SSR snapshot: createLocalStorage returns a no-op manager in Node context,
+    // so manager.get() safely returns defaultValue without accessing localStorage.
     return manager.get();
   });
 

packages/stl/src/lib/window/localStorage.test.ts

@@ -44,9 +44,15 @@ describe('lib/window/localStorage', () => {
     for (const key in mockStorage) delete mockStorage[key];
   });
 
-  it('should throw if window is undefined', () => {
+  it('returns a no-op manager when window is undefined (SSR/SSG context)', () => {
     vi.stubGlobal('window', undefined);
-    expect(() => createLocalStorage(KEY, DEFAULT_VALUE)).toThrow();
+    const manager = createLocalStorage(KEY, DEFAULT_VALUE);
+    expect(manager.key).toBe(KEY);
+    expect(manager.get()).toEqual(DEFAULT_VALUE);
+    expect(() => manager.set({ foo: 'x' })).not.toThrow();
+    expect(() => manager.remove()).not.toThrow();
+    // get() still returns defaultValue after set (no-op in SSR)
+    expect(manager.get()).toEqual(DEFAULT_VALUE);
   });
 
   it('should get default value if empty', () => {

packages/stl/src/lib/window/localStorage.ts

@@ -17,7 +17,8 @@ export interface StorageManager<T> {
 /**
  * Creates a type-safe manager for a localStorage key.
  *
- * This utility is browser-only and will throw if accessed during SSR.
+ * In SSR/SSG context (no window), returns a no-op manager that always
+ * returns the default value. In the browser, uses localStorage as usual.
  * Ensure you use a strict namespace for the key to avoid monorepo collisions.
  * Recommended format: `ermnvldmr/{package}/{path}/{module}`
  * Example: `ermnvldmr/ui/lib/theme`
@@ -31,15 +32,15 @@ export interface StorageManager<T> {
  * const theme = createLocalStorage('ermnvldmr/ui/lib/theme', 'system');
  * console.log(theme.get());
  * ```
- *
- * @throws Error if window or localStorage is undefined.
  */
 export function createLocalStorage<T>(key: string, defaultValue: T): StorageManager<T> {
   if (typeof window === 'undefined' || typeof window.localStorage === 'undefined') {
-    throw new Error(
-      `[createLocalStorage] Attempted to access storage for key "${key}" outside of a browser environment. ` +
-        'This utility is strictly for client-side use.'
-    );
+    return {
+      key,
+      get: () => defaultValue,
+      set: () => { /* no-op in SSR/SSG context */ },
+      remove: () => { /* no-op in SSR/SSG context */ },
+    };
   }
 
   const manager: StorageManager<T> = {