Revise heat storage capacity labels and description

[mabijkerk]

Context

ETModel has sliders that let users limit the output (discharge) capacity of heat storage on the district heating networks — i.e. how much heat can be drawn from storage in a single hour. There is one slider per temperature level (HT, MT and LT).

The slider value is a percentage of the average hourly heat demand on that heat network: a value of 200% means up to twice the average hourly demand can be discharged from storage in a given hour. Limiting this can slow the depletion of heat storage and may force other dispatchable heat sources (e.g. gas heaters) to switch on earlier.

The slider is currently labelled "Output capacity (as % of average hourly load)" with an accompanying description aimed at expert users.

Current shortcoming

1. "% of average hourly load" is ambiguous — load of what? It's not clear that the reference is the total inflexible heat demand on the heat network. A user can easily misread it as a percentage of the storage's own hourly load, which is a completely different and meaningless quantity.

2. The "unlimited by default" claim appears to be incorrect. The description states: "By default, this capacity is unlimited." However, the slider defaults to 300%, which is also the maximum value.

Proposed enhancement

• Relabel the slider to make the reference quantity explicit, e.g. "Discharge capacity (as % of average heat demand on the network)" or "Max heat output (as % of average hourly network demand)".
• Rewrite the description to:
  • Clarify that the percentage is relative to the average hourly heat demand of the heat network (the inflexible demand served by the distribution node), not the storage itself.
  • Correct or remove the "unlimited by default" statement once the actual default behaviour is confirmed. If the default really is meant to be effectively unlimited, reconsider the default/max values so the relationship between "300%" and "unlimited" is clear.

Success criteria

• The slider label unambiguously communicates that the percentage refers to the average hourly heat demand on the heat network.
• The description accurately reflects the model's behaviour — in particular, the default-capacity statement matches what the engine actually does (verified against HeatStorageAdapter / StorageAdapter#capacity_from_other_demand).
• The default and max slider values are intentional and internally consistent with the description.
• Changes applied consistently across the HT, MT, and LT storage sliders.