docs: add a real root README and rewrite the frontend one

The repository had no root README at all, and frontend/README.md was
still the stock Vite template. Add a bilingual (EN/RU) overview covering
the mod, site, and backend plus how they connect (%link, %config
save/load), replace the frontend README with the actual stack, layout,
and scripts, and fix the mod README's broken DEVELOPMENT.md link to
point at DEV_GUIDE.md.

frontend/README.md

@@ -1,32 +1,49 @@
-# React + TypeScript + Vite
+# LoVisual Website
 
-This template provides a minimal setup to get React working in Vite with HMR and some Oxlint rules.
+The frontend for [LoVisual](../README.md) - a marketing site with a live in-game GUI demo,
+download page, documentation, themes/showcase pages, and an account dashboard with a cloud
+config manager. UI is fully bilingual (Russian default, English toggle, persisted in the URL).
 
-Currently, two official plugins are available:
+## Stack
 
-- [@vitejs/plugin-react](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react) uses [Oxc](https://oxc.rs)
-- [@vitejs/plugin-react-swc](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react-swc) uses [SWC](https://swc.rs/)
+- **React 19 + TypeScript + Vite**, package manager: **bun**
+- **Tailwind CSS v4** with custom design tokens (radii, glass panels, control sizing)
+- **TanStack Query** for backend calls, **react-router** for pages
+- **react-i18next** - `ru`/`en` resources per feature, compile-time key parity via `satisfies`
+- **motion/react** for animation, **vitest + Testing Library** for tests
+- **oxlint** for linting
 
-## React Compiler
+## Layout
 
-The React Compiler is not enabled on this template because of its impact on dev & build performances. To add it, see [this documentation](https://react.dev/learn/react-compiler/installation).
-
-## Expanding the Oxlint configuration
-
-If you are developing a production application, we recommend enabling type-aware lint rules by installing `oxlint-tsgolint` and editing `.oxlintrc.json`:
-
-```json
-{
-  "$schema": "./node_modules/oxlint/configuration_schema.json",
-  "plugins": ["react", "typescript", "oxc"],
-  "options": {
-    "typeAware": true
-  },
-  "rules": {
-    "react/rules-of-hooks": "error",
-    "react/only-export-components": ["warn", { "allowConstantExport": true }]
-  }
-}
+```
+src/
+├── app/         router, providers, App shell
+├── features/    one folder per domain (account, cloud, demo, themes, ...)
+│   └── <f>/     api.ts · i18n/{ru,en}.ts · components/ · tests/
+├── pages/       route-level pages composing features
+├── shared/      ui primitives, i18n bootstrap, easter eggs, helpers
+└── test/        vitest setup and utilities
 ```
 
-See the [Oxlint rules documentation](https://oxc.rs/docs/guide/usage/linter/rules) for the full list of rules and categories.
+Feature-folder rules: API calls, translations and components live together; no cross-feature
+imports except through `shared/`.
+
+## Scripts
+
+```bash
+bun install        # install dependencies
+bun run dev        # dev server on http://localhost:5173 (proxies /api to the backend)
+bun run test       # vitest run
+bun run build      # tsc -b + vite build → dist/
+bun run lint       # oxlint
+bun run gen:themes # regenerate theme tokens from the mod palette (scripts/extract-themes.ts)
+```
+
+The dev server expects the Rust gateway on `127.0.0.1:8080` (see [`backend/`](../backend));
+without it, API-backed pages degrade to demo/offline states by design.
+
+## Testing
+
+Unit and component tests are colocated in `features/*/tests/` and `shared/**/tests/`;
+run a single file with `bunx vitest run src/features/account/tests/account.test.tsx`.
+Translation parity (ru ↔ en key sets) is enforced at compile time and in tests.