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/AGENTS.md

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+## Development
+
+The public Astro site is in `website/`. Run its npm and Astro commands from that folder. `frontend/` and `backend/` are reserved for the new consumer application and BFF.
+
+When starting the dev server, use background mode:
+
+```
+astro dev --background
+```
+
+Manage the background server with `astro dev stop`, `astro dev status`, and `astro dev logs`.
+
+## Documentation
+
+Full documentation: https://docs.astro.build
+
+Consult these guides before working on related tasks:
+
+- [Adding pages, dynamic routes, or middleware](https://docs.astro.build/en/guides/routing/)
+- [Working with Astro components](https://docs.astro.build/en/basics/astro-components/)
+- [Using React, Vue, Svelte, or other framework components](https://docs.astro.build/en/guides/framework-components/)
+- [Adding or managing content](https://docs.astro.build/en/guides/content-collections/)
+- [Adding styles or using Tailwind](https://docs.astro.build/en/guides/styling/)
+- [Supporting multiple languages](https://docs.astro.build/en/guides/internationalization/)