engine: show temperature and wall heat in fluid results

Route saved temperature through slices, obstacle surfaces, streamlines and both result views, with availability and model units shared by commands and the UI. Show signed obstacle heat histories per complete face area at the selected frame, leaving unrecorded times uncoloured and retaining the saved slice settings.

Part of #157.

crates/engine/src/catalogue.rs

@@ -696,7 +696,7 @@ pub static CATALOGUE: &[Capability] = &[
         "Streamlines",
         Results,
         "Plots",
-        "A fluid step's streamlines coloured by speed, its velocity or pressure on a slice, and the obstacles coloured by the flow",
+        "A fluid step's velocity, pressure or temperature on slices and obstacles, speed or temperature along streamlines, and signed wall heat per area",
         &["results.slice", "results.surface"],
     ),
     ready("results.export.vtu", "Export VTU", Results, "Files", "Write a solved step as VTK unstructured grids for ParaView"),