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.

docs/features.md

@@ -160,7 +160,7 @@ the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 | Plots | Path Plot — Plot a quantity along a path | coming soon (M9) |  |
 | Plots | Cut — Section cuts through the model | coming soon (M9) |  |
 | Plots | Display Group — Show and hide parts of the model | coming soon (M9) |  |
-| Plots | Streamlines — A fluid step's streamlines coloured by speed, its velocity or pressure on a slice, and the obstacles coloured by the flow | ready | `results.streamlines`, `results.slice`, `results.surface` |
+| Plots | Streamlines — A fluid step's velocity, pressure or temperature on slices and obstacles, speed or temperature along streamlines, and signed wall heat per area | ready | `results.streamlines`, `results.slice`, `results.surface` |
 | Files | Export VTU — Write a solved step as VTK unstructured grids for ParaView | ready | `results.export.vtu` |
 | Files | Read Results — Read results in public formats | coming soon (M9) |  |
 | Files | Convergence — Mesh convergence studies | coming soon (M9) |  |