Add dockerignore, fix Redis image, add troubleshooting docs

- Add .dockerignore for backend-java and frontend (276MB → 336KB)
- Fix Redis image to use full registry path (CRI-O compatibility)
- Update ingress TLS to www only (root domain DNS pending)
- Add comprehensive troubleshooting documentation

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

k8s/ingress.yaml

@@ -16,7 +16,6 @@ spec:
   tls:
     - hosts:
         - www.tasteby.net
-        - tasteby.net
       secretName: tasteby-tls
   rules:
     - host: www.tasteby.net

k8s/redis-deployment.yaml

@@ -15,7 +15,7 @@ spec:
     spec:
       containers:
         - name: redis
-          image: redis:7-alpine
+          image: docker.io/library/redis:7-alpine
           ports:
             - containerPort: 6379
           resources: