perf: reduce RAM usage for 1GB host

- MariaDB: limit innodb buffer pool to 128M, max 20 connections
- Celery worker: concurrency 2→1
- Flower: moved to 'flower' profile (opt-in, not started by default)
  Start with: docker compose --profile flower up -d flower

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

docker-compose.yml

@@ -2,6 +2,7 @@ services:
   db:
     image: mariadb:11.4
     restart: unless-stopped
+    command: --innodb-buffer-pool-size=128M --max-connections=20
     environment:
       MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
       MYSQL_DATABASE: ${DB_NAME}
@@ -73,7 +74,7 @@ services:
         condition: service_healthy
       db:
         condition: service_healthy
-    command: celery -A web.tasks.celery_app worker --loglevel=info --concurrency=2 --queues=default,sync,health,notifications -E
+    command: celery -A web.tasks.celery_app worker --loglevel=info --concurrency=1 --queues=default,sync,health,notifications -E
 
   beat:
     build:
@@ -97,6 +98,7 @@ services:
       context: .
       dockerfile: Dockerfile.web
     restart: unless-stopped
+    profiles: [flower]
     ports:
       - "5555:5555"
     environment: