Add the Next.js web app and shared lesson content.

Move lessons out of the C sources into JSON so the web client can use the same material as the desktop app, and point release builds at desktop/.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/app/networks/page.tsx

@@ -0,0 +1,6 @@
+import { NetworkYearsScreen } from './NetworkYearsScreen';
+
+/** Year picker: year 1 has all 27 lessons, years 2-4 are placeholders. */
+export default function NetworkYearsPage() {
+  return <NetworkYearsScreen />;
+}