infra: clean up Keycloak configuration, enforce consistency in .env, and improve health checks

Streamlined Keycloak configurations with defaults for development and production in `.env`. Added health checks and improved environment variable documentation with comments to differentiate local and server deployments. Ensured compatibility with pre-built registry images.

dc-backend.yaml

@@ -118,11 +118,11 @@ services:
       SPRING_DATASOURCE_USERNAME: "${POSTGRES_USER:-pg-user}"
       SPRING_DATASOURCE_PASSWORD: "${POSTGRES_PASSWORD:-pg-password}"
 
-      # --- REDIS ---
-      SPRING_DATA_REDIS_HOST: "${REDIS_SERVER_HOSTNAME:-redis}"
-      SPRING_DATA_REDIS_PORT: "${REDIS_SERVICE_PORT:-6379}"
-      SPRING_DATA_REDIS_PASSWORD: "${REDIS_PASSWORD:-redis-password}"
-      SPRING_DATA_REDIS_CONNECT_TIMEOUT: "${REDIS_SERVER_CONNECT_TIMEOUT:-5s}"
+      # --- VALKEY (formerly Redis) ---
+      SPRING_DATA_VALKEY_HOST: "${VALKEY_SERVER_HOSTNAME:-valkey}"
+      SPRING_DATA_VALKEY_PORT: "${VALKEY_SERVER_PORT:-6379}"
+      SPRING_DATA_VALKEY_PASSWORD: "${VALKEY_PASSWORD:-}"
+      SPRING_DATA_VALKEY_CONNECT_TIMEOUT: "${VALKEY_SERVER_CONNECT_TIMEOUT:-5s}"
 
       # --- ZIPKIN ---
       MANAGEMENT_ZIPKIN_TRACING_ENDPOINT: "${ZIPKIN_ENDPOINT:-http://zipkin:9411/api/v2/spans}"