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/NetworkYearsScreen.tsx

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+'use client';
+
+import Link from 'next/link';
+
+import { useApp } from '@/app/providers';
+import { TopBar } from '@/components/TopBar';
+import { LockIcon } from '@/components/icons';
+
+/** Only year 1 has content, matching `build_net_years_page` in the desktop app. */
+const YEARS = [1, 2, 3, 4];
+
+export function NetworkYearsScreen() {
+  const { t } = useApp();
+
+  return (
+    <div className="shell">
+      <TopBar title={t('net_years_title')} backHref="/subjects" />
+
+      <main className="page">
+        <div className="page__head">
+          <h1 className="page__title">{t('net_years_title')}</h1>
+          <p className="page__sub">{t('net_years_sub')}</p>
+        </div>
+
+        <div className="grid">
+          {YEARS.map((year) => {
+            const label = t(`net_year${year}`);
+            const locked = year !== 1;
+
+            if (locked) {
+              return (
+                <div className="card card--locked" key={year} aria-disabled>
+                  <span className="row" style={{ color: 'var(--overlay)' }}>
+                    <LockIcon size={22} />
+                  </span>
+                  <h2 className="card__title">{label}</h2>
+                  <p className="card__body">{t('net_year_locked_sub')}</p>
+                </div>
+              );
+            }
+
+            return (
+              <Link className="card card--interactive" href={`/networks/year-${year}`} key={year}>
+                <span className="card__kicker">{year}</span>
+                <h2 className="card__title">{label}</h2>
+              </Link>
+            );
+          })}
+        </div>
+      </main>
+    </div>
+  );
+}

web/src/app/networks/page.tsx

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

web/src/app/networks/year-1/[lesson]/page.tsx

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+import { notFound } from 'next/navigation';
+
+import { getLesson, getLessonIds } from '@/content';
+import { LessonScreen } from '@/components/LessonScreen';
+
+export async function generateStaticParams() {
+  const ids = await getLessonIds('networks');
+  return ids.map((lesson) => ({ lesson }));
+}
+
+export default async function NetworkLessonPage({
+  params,
+}: {
+  params: Promise<{ lesson: string }>;
+}) {
+  const { lesson: id } = await params;
+
+  try {
+    return <LessonScreen lesson={await getLesson('networks', id)} backHref="/networks/year-1" />;
+  } catch {
+    notFound();
+  }
+}

web/src/app/networks/year-1/page.tsx

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+import { notFound } from 'next/navigation';
+
+import { getLessons, getPath } from '@/content';
+import { PathScreen } from '@/components/PathScreen';
+
+export default async function NetworkYear1Page() {
+  const path = await getPath('networks');
+  if (!path) notFound();
+
+  const lessons = await getLessons('networks');
+  const taskCounts = Object.fromEntries(lessons.map((l) => [l.id, l.tasks.length]));
+
+  return (
+    <PathScreen
+      path={path}
+      titleKey="net_years_title"
+      subtitleKey="net_sub"
+      backHref="/networks"
+      hrefBase="/networks/year-1"
+      taskCounts={taskCounts}
+    />
+  );
+}