Prepare product layout and reusable Flutter theme

Relocate the existing Astro website and preserve its assets and hosting configuration. Add the consumer/backend scaffold and themed Flutter package with consumer tests. Related to #1.

website/README.md

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+# SXCHNGE
+
+Astro public website for a crypto-to-fiat exchange. English and Russian, responsive layouts, an illustrative exchange calculator, and explicit company / policy placeholders.
+
+## Development
+
+Node >=22.12.0 (Node >=22.18 for the native TypeScript test runner), npm.
+
+Run these commands from `website/` (use `cd website` from the repository root).
+
+```sh
+npm ci
+npm run dev -- --background --host 127.0.0.1
+npm run test
+npm run build
+```
+
+Use `npm exec astro dev stop` to stop the background preview. Static output is `dist/`. `/` redirects to `/en/`; localized content lives at `/en/` and `/ru/`. Legal placeholders have separate localized routes.
+
+## Content and launch configuration
+
+- Translation source: `src/i18n/copy.ts`.
+- Brand reference: `design/tokens.json`, documented in `design/README.md`.
+- Optional Flutter palette reference: `flutter/brand_palette.dart`. Compatibility does not require identical application styling.
+- Full account URLs: set `PUBLIC_FLUTTER_REGISTER_URL` and `PUBLIC_FLUTTER_LOGIN_URL` at build time, as shown in `.env.example`. Locale is appended as `lang`. Until configured, actions open a clear preview dialog; no credentials are collected.
+- Quote fixtures: `src/lib/quote.ts`. Demo only; no rates are fetched, orders placed, or funds handled.
+- Replace all company placeholders, supply approved legal policies, and confirm supported assets, payout methods, countries, fees and timelines before launch.
+- The preview explicitly uses `noindex,nofollow`. Remove only when launch content is complete, and set the real domain in `astro.config.mjs`.
+
+Fonts are self-hosted with their license. No analytics, third-party trackers, client storage, or authentication backend is included. The website uses Astro's own TypeScript script support; React is unnecessary for the current interactions.