Fix CEFR level selection checkmark

[pirajoke]

Summary

• map persisted Mirror preferences to the UI keys used by Telegram settings
• keep selected depth and CEFR level visible when settings reopen
• add a regression test proving the checkmark moves from Auto to B1

Verification

• RED: focused test failed with adaptive checked instead of B1
• GREEN: focused test passes
• affected suite: 45 tests pass
• full suite: 1230 tests pass, 3 skipped
• compileall and git diff --check pass

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-21T11:59:34.199151Z	2592585	PR opened

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