vocabulary-builder

# Vocabulary Builder Leveled vocabulary with collocations and a file-based Leitner system. Paths are relative to `${CLAUDE_PLUGIN_ROOT}` (if unset, resolve relative to this file). The review state lives in the user's progress directory (`$EXAM_COACH_HOME` or `~/english-exam-coach/`), NOT in the plugin. ## When to use The user asks for new vocabulary at a level or topic, asks to review/quiz existing vocabulary, or meets unknown words in another drill and wants them kept. ## Steps 1. **New set:** identify level (B1–C2) and theme (topic, exam register, e.g. "hedging for C1 writing"). Follow the structure in `data/item-bank/seed/vocabulary-sets.md`: 5–8 items per set, each with collocations and one original example sentence. **Level the words, not just the theme:** pick items whose frequency/register fits the level — B1 high-frequency everyday; B2 common academic (roughly the AWL mid-bands); C1 lower-frequency and abstract; C2 idiomatic/precise nuance — and write the example sentence at that level too, so the set carries level-appropriate language beyond the headword. Note that hedging and precision-verb sets sit at C1/C2, not B1–B2. Open lists like the Academic Word List may be referenced nominatively. 2. **Persist for review:** append new items to `<base>/vocab-box.json` (create if missing). The file is a JSON array; each element is `{"item": ..., "level": ..., "box": 1, "added": "YYYY-MM-DD", "due": "YYYY-MM-DD"}` with ISO dates. Ne...