fix: add openssl to ai-service and fix its DATABASE_URL for Docker

- Dockerfile.ai: install openssl (required by Prisma native engine)
- docker-compose.yml: set DATABASE_URL to postgres:5432 instead of
  localhost, add postgres healthcheck dependency

Co-authored-by: Cursor <cursoragent@cursor.com>

docker/Dockerfile.ai

@@ -1,5 +1,7 @@
 FROM node:20-slim
 
+RUN apt-get update -y && apt-get install -y openssl && rm -rf /var/lib/apt/lists/*
+
 RUN corepack enable && corepack prepare pnpm@9.0.0 --activate
 
 WORKDIR /app