feat: code task required for lesson completion (P0.4)

[gon7187]

Что

• Урок засчитывается только если код-задание решено верно И суммарно >=2/3 (код + хотя бы ещё один вопрос).
• Экзамены не затронуты.
• API submit_lesson: новое поле code_correct; при 2/3 без верного кода сообщение «Для зачёта нужно решить задачу на код».
• Код-задания в контенте переведены на stdout-формат (if/for/while).
• Тесты: test_lesson_requires_correct_code_for_completion (2/3 без кода → fail; код+1 → pass; только код → fail).

Проверка

uv run pytest -q → 10 passed.

Kanban: t_f43de556

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 3648f6f436

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Restore the extended-course test's body

Defining the new test here prematurely ends test_extended_course_unlocks_after_foundation, leaving that test with only a reset while its original assertions are now appended to the code-completion test. Consequently, running the extended-course test by node ID reports success without checking that the extended curriculum unlocks; keep those assertions in their original test and end the new test after its own scenarios.

Useful? React with 👍 / 👎.