- New modules/influxdb.nix: declarative InfluxDB v2 with ZFS-backed
  storage (dick/system/influxdb, bind-mounted to /var/lib/influxdb2)
- monitoring.nix: make influxUrl configurable (default: skydick)
- skydick/default.nix: enable influxdb, point telegraf to localhost
- datapool.nix: document influxdb dataset in hierarchy + creation cmds

Consolidates all monitoring data (door1 + skydick + IoT sensors) into
a single InfluxDB on the ZFS storage server for infinite retention.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>