chore(deps): update postgres docker tag to v18

Author: renovate[bot]

synkronus-portal/docker-compose.yml

@@ -13,7 +13,7 @@
 services:
   # PostgreSQL database
   postgres:
-    image: postgres:17
+    image: postgres:18
     container_name: synkronus-postgres
     environment:
       POSTGRES_USER: postgres

synkronus/docker-compose.dev.yml

@@ -4,7 +4,7 @@
 
 services:
   postgres:
-    image: postgres:17
+    image: postgres:18
     container_name: synkronus-postgres-dev
     environment:
       POSTGRES_USER: postgres

synkronus/docker-compose.example.yml

@@ -71,7 +71,7 @@ services:
 
   # PostgreSQL database
   postgres:
-    image: postgres:17
+    image: postgres:18
     environment:
       # Root PostgreSQL user and password (used to create application databases)
       POSTGRES_USER: postgres