[BOUNTY] Add cross-platform health check fallbacks

[leo202000]

Summary

Add cross-platform fallbacks for check_memory_usage() and check_load_average() so non-Linux environments report useful values instead of generic /proc read failures.

Changes

• check_memory_usage(): tries /proc/meminfo first (Linux), falls back to Windows GlobalMemoryStatusEx API, reports meaningful message if neither available
• check_load_average(): tries /proc/loadavg first (Linux), falls back to os.getloadavg() (Unix/macOS), reports meaningful message if neither available
• JSON and text health-check output remain backward compatible
• Linux behavior unchanged

Testing

• Python syntax validation passed
• Linux path preserved with try/except FileNotFoundError for clean fallback
• Windows path uses ctypes for GlobalMemoryStatusEx
• macOS path uses os.getloadavg()

Checklist

• Relevant modules build locally
• Changes are scoped to the PR purpose
• No external dependencies

[leo202000]

Hi! This PR addresses the bounty issue and is ready for review.

Could you let me know the process for claiming the $50 (LT) bounty once merged? My Base wallet is configured and ready.

Thanks!