docs: Lowest-Node Physical Integration Notes

[jesseray718]

This document is written for people who have almost no money or tools and still want a working MeshCore node.

It focuses on:

• Simple scrap mounting and weather protection
• Co-locating the radio with a passive physical structure (chicken-wire / Node-001 style)
• Clear definition of success at the lowest-node level

Goal: raise the floor for the people with the least resources while staying fully compatible with the existing MeshCore stack.