v0.3.0

Stable release. Promotes 0.3.0-beta.1 to stable after a multi-week live
soak. Headline feature: Time-of-Use (ToU) tariff support — per-tariff
consumption/cost statistics plus per-band rate sensors, with flat-rate contracts
unchanged. No code change vs 0.3.0-beta.1; see the [0.3.0-beta.1] entry below
for the full breakdown.

Time-of-Use caveat. ToU has not been validated against a real AGL ToU
account — the maintainer's live contract is flat-rate, and the original
requester (#82) did not return to test the beta. The flat-rate path is the
soaked, stable path. On ToU contracts the consumption/cost split is driven
by the documented per-interval consumption.type and is expected correct, but
the per-band rate sensors use an unvalidated plan-text heuristic (#90) and
may read unavailable; a sparse-band cumulative-sum edge case is tracked in #114.

Closes #82.

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