fix(security): harden production Docker — bind DB/Redis to localhost, add Redis auth

- Postgres and Redis ports now bind to 127.0.0.1 only, preventing exposure
  to the network even if the host firewall has a gap
- Redis requires a password (REDIS_PASSWORD) via --requirepass; REDIS_URL in
  app and migrator services updated to include the credential
- Redis healthcheck updated to pass -a flag so it still works with auth enabled
- REDIS_PASSWORD added to .env.example with generation hint

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

docker-compose.prod.yml

@@ -5,7 +5,7 @@ services:
     image: postgres:16-alpine
     restart: unless-stopped
     ports:
-      - "${POSTGRES_PORT:-5432}:5432"
+      - "127.0.0.1:${POSTGRES_PORT:-5432}:5432"
     environment:
       POSTGRES_DB: capakraken
       POSTGRES_USER: capakraken
@@ -31,12 +31,12 @@ services:
     image: redis:7-alpine
     restart: unless-stopped
     ports:
-      - "${REDIS_PORT:-6379}:6379"
-    command: redis-server --maxmemory 256mb --maxmemory-policy allkeys-lru
+      - "127.0.0.1:${REDIS_PORT:-6379}:6379"
+    command: redis-server --maxmemory 256mb --maxmemory-policy allkeys-lru --requirepass ${REDIS_PASSWORD}
     volumes:
       - capakraken_prod_redis:/data
     healthcheck:
-      test: ["CMD", "redis-cli", "ping"]
+      test: ["CMD", "redis-cli", "-a", "${REDIS_PASSWORD}", "--no-auth-warning", "ping"]
       interval: 10s
       timeout: 5s
       retries: 5
@@ -50,7 +50,7 @@ services:
       - .env.production
     environment:
       DATABASE_URL: postgresql://capakraken:${POSTGRES_PASSWORD:?set POSTGRES_PASSWORD}@postgres:5432/capakraken
-      REDIS_URL: redis://redis:6379
+      REDIS_URL: redis://:${REDIS_PASSWORD}@redis:6379
       RATE_LIMIT_BACKEND: ${RATE_LIMIT_BACKEND:-redis}
     depends_on:
       postgres:
@@ -68,7 +68,7 @@ services:
       - .env.production
     environment:
       DATABASE_URL: postgresql://capakraken:${POSTGRES_PASSWORD:?set POSTGRES_PASSWORD}@postgres:5432/capakraken
-      REDIS_URL: redis://redis:6379
+      REDIS_URL: redis://:${REDIS_PASSWORD}@redis:6379
       RATE_LIMIT_BACKEND: ${RATE_LIMIT_BACKEND:-redis}
     depends_on:
       postgres: