fix(central-ui): Flow Debugger spawn edges — real arrowhead + bolt badge; spawner picked by trigger attribute

The trigger-cascade (Spawn) edge used a lightning-bolt marker IN PLACE of the arrowhead. On the upward
Tags→Site hop the bolt sat on top of the riser and read as a broken arrow (rig screenshot 2026-09-08).
Every connector now ends in an ordinary arrowhead; the bolt is a badge (circle + bolt) centred on the
connector's vertical run (FlowGraphView.SpawnBadgePoint, kept in step with OrthogonalPath/AsyncPath).

Same screenshot, second defect: the cascade spawned by "RecipeDownloadFlag = false" was drawn from the
LAST write of the burst (RecipeProcessedFlag) because all four writes share a millisecond and the
spawner rule was time-only. FlowGraphBuilder now prefers the parent's last AttributeWrite of the attribute
the child's triggerAttribute names (at or before the child, else the last such write); the time/position
rules remain the fallback when the child names no attribute or the parent never wrote it.

Verified live on the rebuilt rig (DelmiaSim01 / DelmiaReceiverSimulator): both spawn edges show an
arrowhead + badge, the second one originates from the RecipeDownloadFlag write. bUnit + builder tests
updated/added; Playwright FlowDebuggerTests 4/4.

Claude-Session: https://claude.ai/code/session_01NcMG6xXdsJbmD2wYAgkK29

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/FlowGraphView.razor

@@ -17,10 +17,6 @@
             <marker id="fg-arrow-accent" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="8" markerHeight="8" orient="auto-start-reverse">
                 <path d="M 0 0 L 10 5 L 0 10 z" class="fg-arrowhead accent" />
             </marker>
-            @* Trigger spawn (plan D9): a small bolt in place of the arrowhead — this write fired a value-change script. *@
-            <marker id="fg-arrow-spawn" viewBox="0 0 12 14" refX="10" refY="7" markerWidth="12" markerHeight="14" orient="auto-start-reverse">
-                <path d="M 5 1 l -4 6 h 5 l -3 6 l 7 -8 h -5 l 3 -4 z" class="fg-arrowhead spawn" />
-            </marker>
         </defs>
 
         @* Lanes *@
@@ -57,6 +53,17 @@
                 @* Names the branch where it lands: the run carried on without waiting for this. *@
                 @SvgText(tag.X, tag.Y, "fg-edge-tag", "async", dataTest: "flow-edge-tag")
             }
+            @if (SpawnBadgeFor(e) is { } badge)
+            {
+                @* Trigger cascade (plan D9): a bolt badge on the connector itself — this write fired a value-change
+                   script. The edge keeps an ordinary arrowhead; the bolt used to BE the arrowhead, and on the
+                   upward Tags→Site hop it read as a broken arrow (rig, 2026-09-08). *@
+                <g class="fg-spawn-badge" transform="translate(@badge.X @badge.Y)" data-test="flow-edge-spawn">
+                    <title>Trigger cascade: this write fired the script</title>
+                    <circle r="8" class="fg-spawn-badge-bg" />
+                    <path d="M -1 -6 l -4 6 h 5 l -3 6 l 7 -8 h -5 l 3 -4 z" class="fg-spawn-bolt" />
+                </g>
+            }
         }
 
         @* Nodes *@