setup_cell.py: register_with_ddns() called at end of setup — detects
public IP via api.ipify.org, generates TOTP code from DDNS_TOTP_SECRET,
POSTs to DDNS /register, saves token to data/api/.ddns_token (mode 600).
Idempotent: skips if token file already exists. Fails gracefully if
DDNS_TOTP_SECRET is unset or network is unreachable.
scripts/ddns_update.py: standalone script for periodic IP updates.
Reads token from data/api/.ddns_token, fetches current public IP,
compares to cached last IP (data/api/.ddns_last_ip) and calls /update
only when the IP has actually changed.
Makefile: add ddns-update (run update script) and ddns-register (force
re-registration by removing old token then calling register_with_ddns).
Usage: DDNS_TOTP_SECRET=<secret> make ddns-register
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
