Read Teslemetry operation mode from a local Powerwall

[Bre77]

Proposed change

Fourth rung of the local Powerwall data-reading stack for Teslemetry, on top of PW-3.

Routes the operation-mode select's read-back to the local Powerwall on a paired site, reading the verified top-level default_real_mode string from the local config.json coordinator. The existing local-first write path (with cloud fallback) is unchanged.

The preferred export rule stays cloud-only, as its local config mapping is unconfirmed in aiopowerwall. No entities are added.

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