docs(deployment): update memory limits and celery concurrency across all guides

Sync all deployment docs with actual docker-compose.yml values:
- celery-worker: 512→768MB, concurrency 4→2
- db: 512→256MB, celery-beat: 256→128MB, flower: 256→192MB
- Redis maxmemory: 256mb→100mb (matches container mem_limit 128m)
- Add redis-exporter to scaling guide memory budget

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

docs/deployment/infrastructure.md

@@ -409,7 +409,7 @@ services:
   celery:
     build: .
     restart: always
-    command: celery -A app.celery worker --loglevel=info --concurrency=4
+    command: celery -A app.core.celery_config worker --loglevel=info --concurrency=2
     environment:
       DATABASE_URL: postgresql://orion_user:${DB_PASSWORD}@db:5432/orion_db
       REDIS_URL: redis://redis:6379/0
@@ -676,7 +676,7 @@ find $BACKUP_DIR -name "*.sql.gz" -mtime +7 -delete
 **Configuration (`redis.conf`):**
 
 ```ini
-maxmemory 256mb
+maxmemory 100mb
 maxmemory-policy allkeys-lru
 appendonly yes
 appendfsync everysec