CR-1: Add container resource limits to prevent OOM and noisy-neighbor issues

[szachovy]

Problem

No container has memory limits, CPU limits, or PID limits. Without mem_limit, a MySQL query causing excessive memory allocation will OOM-kill the host or steal memory from Redis (Celery broker dies). Without CPU limits, one container can starve others under heavy load. Also a prerequisite for meaningful InnoDB buffer pool tuning (MY-1).

Files: src/container.py, services/mysql-mgmt/docker_compose.yml

Fix

Container	mem_limit	cpus	pids_limit
MySQL Server	2G	2.0	500
MySQL Mgmt	1G	1.0	200
Redis	768M	0.5	100
Superset	2G	2.0	500

Set memswap_limit equal to mem_limit for all containers (no swap).

Acceptance Criteria

• MySQL Server containers: mem_limit=2G, cpus=2.0, pids_limit=500
• MySQL Mgmt containers: mem_limit=1G, cpus=1.0, pids_limit=200
• Redis container: mem_limit=768M, cpus=0.5, pids_limit=100
• Superset container: mem_limit=2G, cpus=2.0, pids_limit=500
• memswap_limit equals mem_limit for all containers (no swap)