chore(env): variables de connexion aux 2 SGBD

.env.example

@@ -1,2 +1,16 @@
 # Variables exposées au client (préfixées NEXT_PUBLIC_)
 # NEXT_PUBLIC_API_URL=http://localhost:3000
+
+# Implémentation repository active : mysql | mongo
+DB_IMPL=mysql
+
+# MySQL (conteneur docker dédié flashcards-mysql, port local 13306)
+MYSQL_HOST=localhost
+MYSQL_PORT=13306
+MYSQL_USER=flashcards
+MYSQL_PASSWORD=flashcards
+MYSQL_DATABASE=flashcards
+
+# MongoDB (conteneur docker dédié flashcards-mongo, port local 127017)
+MONGODB_DATABASE=flashcards
+MONGODB_URI=mongodb://flashcards:flashcards@localhost:127017/flashcards