[LLM] Implement user state database access layer and repositories

[menny]

Summary of Changes

• Implemented pure-JVM SQLite repository interfaces and implementations for user state tables defined in docs/DATA.md:
  • UserWordStateRepository (SqliteUserWordStateRepository) for tracking vocabulary progress (NEW, LEARNING, MASTERED), encounters, vault starred words with saved context sentences, batch status resolution, and status queries.
  • UserCustomTextRepository (SqliteUserCustomTextRepository) for storing, updating, listing, and deleting imported user reading texts and AI-simplified versions.
  • UserDatabase for managing the mutable user SQLite connection and table/index creation.
  • CalqueWordLookupProvider composite implementation uniting DictionaryRepository, FalseCognatesRepository, and UserWordStateRepository into the WordLookupProvider interface required by ReaderEnricher.
• Added unit tests for:
  • User database table and index creation.
  • User word state encounters, vault starring, status updates, and batch lookups with NEW default.
  • Custom texts insertion (auto-generated ID), update, order-by-timestamp listing, and deletion.
  • Composite CalqueWordLookupProvider integration with ReaderEnricher text token enrichment.
• Verified 0 errors across format, format.check, lint, and test gates.