feat(tests): implemented local test DB container for isolation

7project/backend/docker-compose.test.yml

@@ -0,0 +1,20 @@
+version: "3.9"
+services:
+  mariadb:
+    image: mariadb:11.4
+    container_name: test-mariadb
+    environment:
+      MARIADB_ROOT_PASSWORD: rootpw
+      MARIADB_DATABASE: group_project
+      MARIADB_USER: appuser
+      MARIADB_PASSWORD: apppass
+    ports:
+      - "3307:3306"  # host:container (use 3307 on host to avoid conflicts)
+    healthcheck:
+      test: ["CMD", "mariadb-admin", "ping", "-h", "127.0.0.1", "-u", "root", "-prootpw", "--silent"]
+      interval: 5s
+      timeout: 2s
+      retries: 20
+    # Truly ephemeral, fast storage (removed when container stops)
+    tmpfs:
+      - /var/lib/mysql