feat(vocab): sync to 636 verified words (dedup + 13 new entries)

v1.1.0: deduplicate vocabulary (769→611 unique words), add grammar_rules.json (13 rules)

v2.0: expand vocabulary from 431 to 740 verified entries (production DynamoDB export after deduplication and quality audit)

docs: clarify static dataset (431) vs live API (769+), update metadata last_updated

fix: remove dataset_info.splits (SplitInfo mismatch), push 431-entry vocabulary.jsonl, update API word count to 769+

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