feat(health_check): add cross-platform fallbacks for memory and load checks (fixes #1)

[Fuhua-GIF]

Summary

Adds cross-platform fallbacks for check_memory_usage() and check_load_average() in tools/health_check.py, as requested in #1.

Changes

• Updated tools/health_check.py:

  • check_memory_usage(): Keeps /proc/meminfo on Linux; falls back to psutil, then Windows GlobalMemoryStatusEx, then macOS sysctl+vm_stat, then generic warning
  • check_load_average(): Keeps /proc/loadavg on Linux; falls back to os.getloadavg() (macOS/Unix), then psutil.getloadavg(), then Windows CPU% proxy, then generic warning
  • All fallbacks return the same (status, detail, value) tuple format for backward compatibility
  • Linux behavior is unchanged

• Added tests/test_health_check_fallback.py: 5 tests covering:

  1. Memory check returns valid tuple
  2. Load check returns valid tuple
  3. Memory fallback works when /proc/meminfo is missing
  4. Load fallback works when /proc/loadavg is missing
  5. Backward compatibility (output format preserved)

Fallback Behavior

Platform	Memory Check	Load Check
Linux	/proc/meminfo (unchanged)	/proc/loadavg (unchanged)
macOS	sysctl + vm_stat	os.getloadavg()
Windows	GlobalMemoryStatusEx (ctypes)	psutil.cpu_percent() or warning
Other	psutil if available	os.getloadavg() if available

Checklist

• check_memory_usage() keeps /proc/meminfo on Linux, has non-Linux fallback
• check_load_average() keeps /proc/loadavg on Linux, falls back to os.getloadavg()
• Focused tests added simulating missing /proc files
• JSON and text output remain backward compatible
• PR description explains fallback behavior and validation

Fixes #1