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>

tools/extract/i18n.mjs

@@ -0,0 +1,35 @@
+import { readFileSync } from 'node:fs';
+import { parseArray } from '../lib/cparse.mjs';
+
+/**
+ * `tr_ui` holds UI chrome keyed by short identifiers; `tr_content` holds
+ * lesson text keyed by the Czech string itself (its `cs` column is usually
+ * NULL, meaning "the key already is the Czech text").
+ */
+function toTable(entries, { keyIsCzech }) {
+  const cs = {};
+  const en = {};
+
+  for (const row of entries) {
+    if (!Array.isArray(row)) continue;
+    const [key, csText, enText] = row;
+    if (key === null || key === undefined) continue; // terminator
+
+    cs[key] = csText ?? (keyIsCzech ? key : null);
+    if (enText !== null && enText !== undefined) en[key] = enText;
+  }
+
+  // A null Czech value in tr_ui would render as an empty label; drop it.
+  for (const k of Object.keys(cs)) if (cs[k] === null) delete cs[k];
+
+  return { cs, en };
+}
+
+export function extractI18n(desktopDir) {
+  const src = readFileSync(`${desktopDir}/i18n.c`, 'utf8');
+
+  return {
+    ui: toTable(parseArray(src, 'tr_ui'), { keyIsCzech: false }),
+    content: toTable(parseArray(src, 'tr_content'), { keyIsCzech: true }),
+  };
+}