Fix redis service container port mapping to 6379:6379

redis_cache.py hardcodes localhost:6379; dynamic port mapping would
miss it. Fixed mapping ensures the service is reachable as expected.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: wasade

.github/workflows/main.yml

@@ -76,7 +76,7 @@ jobs:
       redis:
         image: redis
         ports:
-          - 6379/tcp
+          - 6379:6379
         options: >-
           --health-cmd "redis-cli ping"
           --health-interval 10s