[plbogen2]

Summary

Closes #9.

This pull request adds an integration testing tier for database migrations and indexer projections against PostgreSQL. The suite exercises event ingestion, foreign key tolerance, and checkpoint persistence to verify that the indexer handles out-of-order streams without corrupting ledger state. All tests pass.

Key Changes

• Add migration runner script pnpm run db:migrate. It applies database/migrations/001_create_tables.sql and database/migrations/002_create_protocol_tables.sql in numeric sequence.
• Add integration test suite in services/indexer/test/database-integration.test.ts. Tests require PostgreSQL.
• Export projectEvents in services/indexer/src/watcher.ts. This allows testing multi-event batches that write to vaults and vault_events.
• Update database/schema/README.md. The document explains migration commands and integration test execution.

Test Coverage

• Idempotent replay: Replaying duplicate Soroban event_id records ignores redundant writes and preserves exact 128-bit base unit amounts (numeric(40,0)).
• Batch coherence: Processing an initialize event alongside a deposit event in a single batch populates both vaults and vault_events records.
• Foreign key tolerance: Events arriving before the corresponding vault row project successfully into the database without dropping records.
• Checkpoint persistence: Checkpoint save and load cycles round-trip through indexer_checkpoints at Number.MAX_SAFE_INTEGER (9_007_199_254_740_991). Out-of-range ledgers narrow to 0.
• Hermetic default: The integration suite skips execution when database environment variables are unset. Offline runs remain hermetic.