- New UnitBuilder component with language pair selector (DE⇄EN, ES, FR, etc.)
- Manual word entry form with auto-suggest from Kaikki dictionary (6M words)
- "No results" prompt to add multi-word terms (e.g. "schottisches Hochland")
- New backend endpoint GET /vocabulary/lookup-translation (any→any via EN hub)
- Updated POST /vocabulary/units: accepts custom_words + source_lang/target_lang
- Split unit endpoints into vocabulary/unit_api.py (500 LOC budget)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>