chore(images): pin service image updates

Replace floating service images with reviewable tags or digests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

edu_master/compose.yaml

@@ -1,6 +1,6 @@
 services:
   redis:
-    image: redis:alpine
+    image: redis:8.0.3-alpine
     restart: unless-stopped
     volumes:
       - redis-data:/data
@@ -11,7 +11,7 @@ services:
       retries: 5
 
   playwright-service:
-    image: mcr.microsoft.com/playwright:v1.56.0-jammy
+    image: mcr.microsoft.com/playwright:v1.56.1-jammy
     restart: unless-stopped
     command: npx -y playwright@1.56.0 run-server --port 3000 --path /ws