Flow: count generation meters as sources (grid + solar → house)

A meter's flow value is now its throughput — consumption OR generation output —
so a generation meter (solar) acts as a source that can feed downstream meters.
Setting a load meter's upstream to {grid, solar} now splits its consumption
across both proportionally, and the remainder under the sources (grid + solar −
load) surfaces as "Other" = export + battery/inverter losses. Negative values
(savings/balance virtuals) are clamped to 0 (a ribbon can't be negative). The
per-type KPI is relabelled "Top-level throughput" since it now spans generation.

Test: Generation_meter_counts_as_source (grid 75 + solar-gen 30 → house 40 →
28.57/11.43 split, 65 remainder). 69 Core + 48 Integration = 117 green.
Live-verified: electricity flow now shows Solar 1/2 as source nodes.

Claude-Session: https://claude.ai/code/session_01Lz2RqAsnQhetqWNoCDfexK

src/App/Components/Pages/EnergyView.razor

@@ -33,7 +33,7 @@ else
     <MudGrid Class="mb-2">
         <MudItem xs="12" sm="4">
             <MudPaper Class="pa-4" Elevation="2">
-                <MudText Typo="Typo.overline" Color="Color.Secondary">Top-level consumption</MudText>
+                <MudText Typo="Typo.overline" Color="Color.Secondary">Top-level throughput</MudText>
                 <MudText Typo="Typo.h5">@Format.Number(_graph.Total, 0) @_graph.Unit</MudText>
             </MudPaper>
         </MudItem>