cable-sizing: trigger on both cable columns, calculator icon

Trigger now matches cableSummary OR cableCrossSection so it still
shows up regardless of which cable-related column a user has visible
(column visibility is a per-browser preference in this app, not fixed
- see docs/cable-sizing-module.md coupling note). Icon changed to a
calculator glyph.

src/app/globals.css

@@ -1228,7 +1228,7 @@ a.kpi:hover {
 }
 
 .tree-grid .cell-cable-sizing-trigger::after {
-  content: " ⚡";
+  content: " 🧮";
   font-size: 0.8em;
   opacity: 0.7;
 }

src/frontend/components/circuit-tree-editor.tsx

@@ -4277,7 +4277,7 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
                         row.rowType !== "deviceRow"
                     );
                     const isCableSizingTrigger = Boolean(
-                      column.key === "cableSummary" &&
+                      (column.key === "cableSummary" || column.key === "cableCrossSection") &&
                         row.circuit &&
                         row.rowType !== "deviceRow"
                     );