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

backup.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+BACKUP_DIR="./backups"
+DATE=$(date +%Y-%m-%d_%H%M%S)
+
+mkdir -p "$BACKUP_DIR"
+
+echo "==> Dumping all databases..."
+docker compose exec -T postgres pg_dumpall -U admin > "${BACKUP_DIR}/all-databases-${DATE}.sql"
+
+echo "==> Backup saved to ${BACKUP_DIR}/all-databases-${DATE}.sql"
+
+# Garder les 7 derniers backups
+ls -t "${BACKUP_DIR}"/all-databases-*.sql | tail -n +8 | xargs -r rm --
+echo "==> Old backups cleaned (keeping last 7)."