feat(database): add PostgreSQL + Redis + MariaDB shared database layer

[zero-logic0316]

📦 Database Layer — PostgreSQL + Redis + MariaDB

One-click deployable database layer for Homelab Stack.

File	Purpose
docker-compose.yml	Core orchestration with resource limits & healthchecks
.env.example	Environment variable template
healthcheck.sh	One-command health check
README.md	Full deployment guide
init/postgres/01-init.sql	PostgreSQL init (uuid-ossp, pg_stat_statements)
init/mariadb/01-init.sql	MariaDB init (utf8mb4)
conf/redis/redis.conf	Redis custom config (persistence, security)
conf/mariadb/my.cnf	MariaDB custom config (InnoDB tuning)

Quick Start

cd database
cp .env.example .env
docker compose up -d
chmod +x healthcheck.sh && ./healthcheck.sh

Closes Database Layer Bounty ($130 USD)