fix(api): support macOS hosts in server system stats monitoring

[chbndrhnns]

Closes #608

Summary

When connecting a macOS (Darwin) host via SSH (e.g. a MacBook or Mac mini), the Server Overview page showed - for CPU, Memory, Disk, and Uptime.

The background metrics streaming endpoint (GET /system/monitor/stream) runs STATS_COMMAND on an interval over SSH to collect live host statistics. The command was hardcoded for Linux and relied on /proc/stat, /proc/meminfo, /proc/uptime, /proc/loadavg, and df -B1 /. On macOS:

• /proc does not exist.
• df -B1 fails with df: illegal option -- B.

This caused STATS_COMMAND to fail on Darwin hosts, preventing the stats SSE event from emitting valid JSON and leaving the frontend cards in a perpetual empty state (-).

Changes

• Updated STATS_COMMAND in apps/api/src/modules/system/server-check.controller.ts to detect the OS via [ "$(uname -s)" = "Darwin" ]:
  • Darwin (macOS):
    • CPU & Load Average: Samples CPU utilization and load averages via iostat -c 2 (falling back to sysctl -n vm.loadavg for load averages if needed).
    • Memory: Probes total RAM via sysctl -n hw.memsize and available memory via vm_stat ((free + inactive + speculative) * pagesize).
    • Disk: Probes root filesystem via POSIX-standard df -Pk / (1024-byte blocks), computing total, used, and available bytes.
    • Uptime: Computes seconds since boot using sysctl -n kern.boottime and current timestamp.
  • Linux:
    • Continues to use /proc/stat, /proc/meminfo, /proc/uptime, /proc/loadavg, and POSIX df -Pk / with safe fallbacks.
• Added unit test apps/api/test/modules/system/server-monitoring-command.test.ts verifying structural integrity and execution against the host.

Tests

• Verified STATS_COMMAND execution on macOS (Darwin), confirming valid JSON output with all expected fields (cpu, memTotal, memUsed, memAvail, diskTotal, diskUsed, diskAvail, uptime, load1, load5, load15).
• Added unit test in apps/api/test/modules/system/server-monitoring-command.test.ts.