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

init/01-create-databases.sql

@@ -0,0 +1,20 @@
+-- Ce script est execute automatiquement au premier lancement de PostgreSQL
+-- (uniquement si le volume data/ est vide)
+--
+-- Ajouter ici les bases et users pour chaque application.
+
+-- SIRH Production
+CREATE USER sirh_prod WITH PASSWORD 'change-me';
+CREATE DATABASE sirh_prod OWNER sirh_prod;
+
+-- SIRH Recette
+CREATE USER sirh_recette WITH PASSWORD 'change-me';
+CREATE DATABASE sirh_recette OWNER sirh_recette;
+
+-- Ferme Production
+CREATE USER ferme_prod WITH PASSWORD 'change-me';
+CREATE DATABASE ferme_prod OWNER ferme_prod;
+
+-- Ferme Recette
+CREATE USER ferme_recette WITH PASSWORD 'change-me';
+CREATE DATABASE ferme_recette OWNER ferme_recette;