Read Teslemetry grid status from a local Powerwall

[Bre77]

Proposed change

Second rung of the local Powerwall data-reading stack for Teslemetry, on top of PW-1.

Routes the grid status binary sensor to the local-first live coordinator on a paired site, so it reads from the LAN gateway with cloud fallback. Backup capable, grid-services active, storm-watch active and grid-services-enabled stay cloud-sourced, as the local gateway has no equivalent. No entities are added.

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