1. Removed stale 'explanations' export that broke build
2. Explanation banner now spans full width ABOVE the 2/3+1/3 layout
so exercise cards and native words start at the same height
3. Both columns use items-start for visual alignment
4. Impressum link added at bottom of learn layout
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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