fix(docker): fix flower and redis-exporter healthchecks

Flower: use /healthcheck endpoint (auth-exempt) instead of root URL.
Redis-exporter: switch to alpine image (has wget) and verify redis_up
in /metrics instead of non-existent /health endpoint.

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

docker-compose.yml

@@ -130,7 +130,7 @@ services:
         condition: service_healthy
     mem_limit: 192m
     healthcheck:
-      test: ["CMD-SHELL", "curl -f http://localhost:5555/ || exit 1"]
+      test: ["CMD-SHELL", "curl -f http://localhost:5555/healthcheck || exit 1"]
       interval: 30s
       timeout: 10s
       retries: 3
@@ -231,7 +231,7 @@ services:
       - monitoring
 
   redis-exporter:
-    image: oliver006/redis_exporter:latest
+    image: oliver006/redis_exporter:alpine
     restart: always
     profiles:
       - full
@@ -244,7 +244,7 @@ services:
         condition: service_healthy
     mem_limit: 32m
     healthcheck:
-      test: ["CMD-SHELL", "wget -qO- http://localhost:9121/health || exit 1"]
+      test: ["CMD-SHELL", "wget -qO- http://localhost:9121/metrics | grep -q 'redis_up 1' || exit 1"]
       interval: 30s
       timeout: 10s
       retries: 3