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/.prettierrc.json

@@ -0,0 +1,5 @@
+{
+  "plugins": ["prettier-plugin-astro"],
+  "singleQuote": true,
+  "overrides": [{ "files": "*.astro", "options": { "parser": "astro" } }]
+}