Build all apps from Markdown content; Compose Desktop replaces GTK on Linux and Windows

- content/ + scripts/build-content.py produce content.json for every app
- stable lesson IDs with one-time progress migration (Swift, Kotlin)
- shared answer-check tests (tests/answers.json) for Kotlin and Swift
- android/desktop: Compose app with updater, speech and GTK progress import
- CI packages AppImage and Windows zip with ProGuard, runs the tests

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

content/nemcina/ucebnice/03-bei-uns-zu-hause/09-kein-nicht.en.md

@@ -0,0 +1,14 @@
+---
+popis: Choose kein/keine/keinen/nicht.
+---
+
+# Překlady
+
+| Česky | Anglicky |
+|---|---|
+| Mluvíš španělsky? – Ne, nemluvím španělsky. | Do you speak Spanish? – No, I don't speak any Spanish. |
+| Máš bratra? – Ne, nemám bratra. | Have you got a brother? – No, I haven't got a brother. |
+| Je v Opavě zoo? – Ne, v Opavě žádná zoo není. | Is there a zoo in Opava? – No, there is no zoo in Opava. |
+| Jdeš do bazénu? – Ne, do bazénu nejdu. | Are you going to the swimming pool? – No, I am not going to the swimming pool. |
+| Rád chodí na túry? – Ne, nerad chodí na túry. | Does he like hiking? – No, he does not like hiking. |
+| Navštívíš dnes zámek? – Ne, dnes nenavštívím žádný zámek. | Are you visiting a castle today? – No, I am not visiting a castle today. |