v0.2.0

What's New

Database module (database)

• DatabaseService — persist words and translations to Neon PostgreSQL
• CachedDatabaseService — LRU-cached variant for read-heavy workloads
• ExerciseProgressStore — per-user per-exercise score tracking
• Neon backend with asyncpg, abstract backend ABC for extensibility
• Testing utilities (drop_all_tables, reset_database, helpers)

Sampling module (sampling)

• WordSampler — weighted word sampling with adversarial distractor selection

Docs

• Added DATABASE_URL to ENV_VARS.md
• Added sampling module to README
• Updated database module description in README
• NEON.md with full Neon PostgreSQL setup instructions

Tests

• 133 unit tests passing
• Integration and e2e tests for database and sampling modules