Adds two new Prometheus metrics for UCI (UniFi Cable Internet) devices:
- unpoller_device_ci_state_operational (gauge): 1 if DOCSIS CI state ==
"Operational", else 0. Suitable for alerting on cable link health.
- unpoller_device_ci_state_info (gauge=1, info-style): exposes the full
DOCSIS CI state table as labels (ci_state, ci_sw_dl_status, ci_mac,
ci_version, ci_mode) for diagnostic dashboards.
The controller does expose a top-level `internet` boolean on UCI
devices, but it is not a reliable WAN-reachability signal — it stays
false even when the cable link is fully operational and the upstream
WAN is up. The UCI is a cable bridge with no independent internet-
reachability probe; real WAN health lives on the upstream gateway
(e.g. UDM wan1.up).
The ci_state field from ci_state_table IS reported reliably and is the
correct source-of-truth for DOCSIS link health.
Verified on a UCI in Operational state (ci_mode=D3.1).
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