feat(plan): show the actual planned charge/export rate in the hover text

[chalfontchubby]

Summary

Closes #4596. Adds the planned charge/export rate (kW) to the plan's per-slot hover/click text, alongside the existing rate (p/kWh) info. gcoan agreed hover text over cluttering the state cell/snail symbol.

• Export: reuses the existing fractional-limit encoding that already drives the snail symbol (limit's fractional part = tens-of-percent rate reduction) - battery_rate_max_export * (1 - (limit - int(limit))). No new computation, just surfacing a value the code already derives elsewhere (execute.py/prediction.py).
• Charging: has no equivalent fixed encoding - low power charging (set_charge_low_power) throttles the rate dynamically per-minute rather than storing a reduced value per window. Added get_charge_rate_kw() in output.py, which recomputes the actual rate via find_charge_rate() (the same function the prediction engine itself uses) so the low-power case shows the real throttled rate rather than the nameplate max, which would otherwise be actively misleading during a slow-charge slot.

Test plan

• ./run_all --test plan_why_reason - extended with two new scenarios: a fractional/slow export limit showing the reduced rate, and a low-power charge slot showing a throttled rate below the nameplate max (not just the simple full-rate case)
• Existing Chrg/Exp reason-param assertions updated to include the new rate_kw param
• ./run_all --quick passes
• ./run_pre_commit passes

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR enhances Predbat’s HTML plan “why” (hover/click) text by including the planned charge/export power rate (kW) alongside the existing price-rate (p/kWh), improving visibility when slow/limited modes are active.

Changes:

• Added rate_kw to the charge_low_rate and export_high_rate reason templates and per-slot reason params.
• Introduced get_charge_rate_kw() to recompute the effective charge rate (including low-power throttling) via find_charge_rate().
• Extended test_plan_why_reason to assert the new rate_kw param and to cover slow export + low-power charge scenarios.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
apps/predbat/output.py	Adds rate_kw into plan reason templates/params; introduces get_charge_rate_kw() and computes export rate_kw from fractional export limit encoding.
apps/predbat/tests/test_plan_why_reason.py	Updates assertions to include rate_kw and adds scenarios for throttled charge and fractional-limit export.

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