Add a track_degraded parameter to IntervalPool.get_intervals so service calls
(track_degraded=False) never flip the coordinator's sensor-health flags or use
the covers-current-interval cache fallback; authentication errors still
propagate. All price-fetching services now go through
async_fetch_service_intervals and return a structured response with a
top-level success flag: success=false with reason="price_data_unavailable" on
a real API outage, and success=true (possibly empty) otherwise.
Impact: Action calls (get_price, find_cheapest_*, plan_charging) always return
the expected shape, never impair sensors during a Tibber outage, and let
automations distinguish an outage from "no data yet".
Accepts battery parameters (capacity, current/target SoC, max power) and
returns a cost-minimized charging schedule with per-interval power, SoC
progression, and total cost — no manual duration calculation needed.
Supports fixed, continuous (min_charge_power_w), and stepped
(charge_power_steps_w) charging modes, deadline-aware two-pass planning
(must_reach_soc + must_reach_by / must_reach_by_event), and round-trip
economics (expected_discharge_price, reserve_for_discharge,
max_cost_per_kwh) for arbitrage use cases. Includes min_charge_duration
and max_cycles_per_day constraints.
Groups deadline fields (must_reach_soc_*, must_reach_by,
must_reach_by_event) into a dedicated section so a deadline use case can
be configured in one place. Battery section lists capacity before the
percent SoC fields that depend on it. Response exposes stable reason
codes (already_at_target, energy_unreachable, energy_unreachable_by_
deadline, no_intervals_after_economic_filter, …) documented in the
service description and user docs.
