Shelly migration & Drive watchdog cron by explicit watchdog_type

[fe51]

Summary

Replaces the implicit "is pi_zero_hostname set?" logic for choosing a Pi's reboot/watchdog behaviour with an explicit watchdog_type variable. This adds first-class support for the new Shelly watchdog alongside the existing pi-zero watchdog and the plain nightly-reboot fallback, and makes the cron configuration converge cleanly when a host's type changes.

watchdog_type values

• no_watchdog — nightly reboot cron (shutdown -r at midnight), no watchdog
• pi_zero — pi-zero watchdog
• shelly — Shelly relay watchdog

Changes

• engine_cron
  • Cron jobs are now selected by watchdog_type. Each job is paired with an explicit removal task so switching type (e.g. pi_zero → shelly) tears down the
    stale job/.env instead of leaving it behind.
  • Reboot cron and watchdog cron are mutually exclusive.
  • New watchdog_shelly.env.j2 template (SHELLY_IP, SHELLY_OUTPUT_ID, CAM_IPS derived from config_json).
  • New defaults: watchdog_main_script map (pi_zero/shelly script paths), shelly_ip (default 192.168.1.97), shelly_output_id (default 0).
  • Watchdog script paths updated to the new pyro-engine watchdog/ layout (zero/ and shelly/ subdirs, per pyro-engine PR #374).
• check_vars
  • Asserts watchdog_type is defined and one of the three valid values on every engine host.
  • Fails fast if watchdog_type == pi_zero but pi_zero_hostname is unset.
• pi_zero_watchdog
  • pi_zero_watchdog_script path updated to watchdog/zero/pi_zero/watchdog.py.

Notes / dependencies

• Requires the matching pyro-engine watchdog directory layout (watchdog/zero/..., watchdog/shelly/...) to be merged
• shelly_ip defaults to a fixed LAN address by convention; override per-host for stations that differ.