Pin the Compose project name to php-project-manager

Was derived from the directory name (php-todo-list). Containers, volumes and
network are now prefixed php-project-manager_ regardless of the directory.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,3 +1,5 @@
+name: php-project-manager
+
 services:
   app:
     build: .