feat(backend): migrate to PostgreSQL with connection pooling, indexs and health check

[JohnOluB]

PR Description

---

Backend: PostgreSQL migration with connection pooling and query optimization

Closes #204

What this PR does

Completes the end-to-end migration from SQLite (development) to PostgreSQL (production), fulfilling every acceptance criterion in issue #204.

Files changed

File | Change -- | -- src/data-source.ts | Switched type to postgres, added SlowQueryLogger, pool extra config src/app.module.ts | Switched TypeORM to postgres, pool startup log, imports HealthModule src/migrations/1774364374007-PostgreSQLMigration.ts | New — full PostgreSQL DDL for all 13 entities, all required indexes src/modules/health/health.{controller,service,module}.ts | New — GET /health returning DB connectivity + pool stats .env.example | Added DATABASE_URL, DB_HOST/PORT/USERNAME/PASSWORD/NAME, DB_POOL_* vars docs/POSTGRES_MIGRATION.md | New — step-by-step migration guide for existing deployments

Key technical decisions

SQLite → PostgreSQL DDL changes: Every datetime → timestamptz, boolean DEFAULT (1)/(0) → DEFAULT true/false, varchar PRIMARY KEY → uuid DEFAULT gen_random_uuid(), all SQLite temporary_* table tricks removed (PostgreSQL supports ALTER TABLE directly).

Connection pooling: Configured via TypeORM's extra key which passes options directly to the underlying pg pool driver — same as pg-pool options. Pool stats are logged on startup and exposed on GET /health.

Slow query logging: A custom SlowQueryLogger class implements TypeORM's Logger interface. It's only activated when NODE_ENV=development via maxQueryExecutionTime: 500.

Indexes added (all required by #204):

• IDX_users_walletAddress — unique, auth lookups
• idx_escrows_status, idx_escrows_created_at, idx_escrows_expires_at — dashboard + scheduler
• IDX_parties_walletAddress — user's escrow lookup
• IDX_escrow_events_escrowId_createdAt — composite, timeline queries
• IDX_notification_userId_read — composite, unread count queries

[drips-wave]

@JohnOluB Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[JohnOluB]

Kindly review pr @Cedarich

[JohnOluB]

Review Pr @Cedarich

[JohnOluB]

Review pr @Cedarich

[Cedarich]

@JohnOluB

[JohnOluB]

@JohnOluB

Please review @Cedarich