fix(docker): macOS compatibility for monitoring containers

Summary

node-exporter and cadvisor containers now work on macOS Docker Desktop.

Root Cause

The rslave mount propagation (/:/host:ro,rslave) is not supported on macOS Docker Desktop, causing node-exporter to fail immediately with exit code 1.

Solution

Removed rslave from node-exporter volume mount. Containers now start on all platforms.

Trade-off

Without rslave, dynamically mounted filesystems (USB drives, NFS mounts added after container start) won't be monitored. This rarely matters for PostgreSQL monitoring.

Test plan

• docker compose up -d node-exporter cadvisor on macOS - both start with exit code 0
• CLI tests pass (184 pass, 0 fail)

🤖 Generated with Claude Code

Related to https://gitlab.com/postgres-ai/platform/-/issues/346