db: drizzle schema matching spec 02, initial migrations, settings service

Migration 0000 enables citext; 0001 creates all 39 tables. DB tests use a
throwaway database per file (TEST_DATABASE_URL, derived from .env in dev,
a postgres service in CI). Decision 0002: pg driver and @fastify/cookie.

Task: M1-T1

apps/api/drizzle.config.ts

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import { defineConfig } from 'drizzle-kit';
+
+export default defineConfig({
+  dialect: 'postgresql',
+  schema: './src/db/schema.ts',
+  out: './src/db/migrations',
+  casing: 'snake_case',
+});