fix(db): migrate from SQLite to PostgreSQL for production readiness

[Chrogend]

Overview

This PR completes the migration from SQLite to PostgreSQL for production readiness. The Prisma schema and migrations were already targeting PostgreSQL, but the raw database access layer (src/db.js) still used SQLite via the sqlite3 package with generic-pool. This PR replaces the entire SQLite stack with pg (node-postgres) and updates all SQL queries to use PostgreSQL-compatible syntax.

Related Issue

Closes #502

Changes

Database Layer

• [REWRITE] src/db.js

  • Replaced sqlite3 + generic-pool with pg (node-postgres) Pool
  • Schema initialization uses PostgreSQL-compatible CREATE TABLE IF NOT EXISTS with TIMESTAMPTZ
  • Added NODE_ENV=test guard to prevent process.exit(1) during test runs
  • Exports poolGet, poolRun, poolAll with PostgreSQL query interface

• [MODIFY] package.json

  • Removed sqlite3 dependency
  • Added pg (node-postgres) dependency

SQL Query Updates

• [MODIFY] server.js

  • Converted ? placeholders to $1 PostgreSQL syntax
  • Replaced COLLATE NOCASE with ILIKE for case-insensitive search
  • Added P2002 error code handling for PostgreSQL unique constraint violations

• [MODIFY] src/routes/v1/userRoutes.js

  • All SQL queries converted to PostgreSQL syntax ($1 placeholders, ILIKE)

• [MODIFY] src/routes/v1/webhookRoutes.js

  • SQL queries converted to PostgreSQL syntax

• [MODIFY] src/routes/v1/statsRoutes.js

  • Column aliases quoted with double quotes for PostgreSQL compatibility

• [MODIFY] src/webhookWorker.js

  • All SQL queries converted to PostgreSQL syntax

Docker Compose

• [MODIFY] docker-compose.test.yml
  • Added postgres-test service (PostgreSQL 16 Alpine)
  • Updated api-test service to use DATABASE_URL pointing to PostgreSQL instead of DB_PATH for SQLite
  • Added depends_on with health check condition

Tests

• [MODIFY] All test files (server.test.js, register-endpoint.test.js, register-multisigner.test.js, helmet.test.js, rate-limit.test.js, sentry.test.js)
  • Replaced sqlite3 and generic-pool mocks with pg Pool mocks

Verification Results

Test Suites: 24 passed, 24 total
Tests:       352 passed, 352 total

Acceptance Criteria

• Prisma schema updated to PostgreSQL -- Already migrated (provider = "postgresql")
• Migrations re-generated for PostgreSQL -- Already generated (migration_lock.toml = "postgresql")
• Docker-compose updated for local testing -- docker-compose.test.yml now uses PostgreSQL
• Raw SQLite queries replaced with PostgreSQL -- All poolGet/poolRun/poolAll queries converted
• Tests pass -- 352/352 tests passing

Impact

• Unlocks row-level locking, high concurrency, and robust scaling for the database layer
• Removes SQLite dependency entirely from the production code path
• Maintains backward compatibility with existing Prisma-based queries

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