fix: resolve bounty issue #1 - add cross-platform health check fallbacks

[lequangsang01]

Summary

This PR adds cross-platform fallbacks for check_memory_usage() and check_load_average() in tools/health_check.py, so non-Linux environments (macOS, Windows) report meaningful diagnostics instead of generic /proc read failures.

Changes

tools/health_check.py

• check_memory_usage(): Refactored into a chain of fallbacks:

  1. _check_memory_linux() — reads /proc/meminfo (Linux)
  2. _check_memory_psutil() — uses psutil.virtual_memory() if available
  3. _check_memory_platform() — uses sysctl + vm_stat (macOS)

• check_load_average(): Refactored into a chain of fallbacks:

  1. _check_load_linux() — reads /proc/loadavg (Linux)
  2. _check_load_getloadavg() — uses os.getloadavg() (macOS, Unix)

tools/test_health_check.py (new)

13 unit tests covering:

• Linux /proc/meminfo and /proc/loadavg parsing
• Fallback behavior when /proc files are missing
• os.getloadavg() fallback for load average
• Backward compatibility (JSON output format, return types)

Validation

• All 13 tests pass: python3 tools/test_health_check.py -v
• Verified on macOS (Apple Silicon): memory reports 68.9% used (11GB/16GB), load reports Load: 4.0 (25% of 16 cores)
• JSON and text output remain backward compatible

Closes

Closes #1