betterNAS Node Agent

Go service that runs on the NAS machine.

For the scaffold it does two things:

serves GET /health
serves a WebDAV export at /dav/
optionally serves multiple configured exports at deterministic /dav/exports/<slug>/ paths via BETTERNAS_EXPORT_PATHS_JSON
registers itself with the control plane and syncs its exports when BETTERNAS_CONTROL_PLANE_URL is configured
uses BETTERNAS_USERNAME and BETTERNAS_PASSWORD both for control-plane login and for local WebDAV basic auth

This is the first real storage-facing surface in the monorepo.

The user-facing binary should be distributed as betternas-node.