feat : initial PostgreSQL infrastructure setup

- docker-compose with postgres:16-alpine
- Init script to create databases (SIRH + Ferme, prod + recette)
- Deploy script with readiness check
- Backup script with rotation (keeps last 7)
- Auto-tag CI workflow
- Full deployment documentation

deploy.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+echo "==> Pulling PostgreSQL image..."
+docker compose pull
+
+echo "==> Starting PostgreSQL..."
+docker compose up -d
+
+echo "==> Waiting for PostgreSQL to be ready..."
+until docker compose exec -T postgres pg_isready -U admin > /dev/null 2>&1; do
+    sleep 1
+done
+
+echo "==> PostgreSQL is ready."
+docker compose exec -T postgres psql -U admin -c "SELECT version();"