cable-sizing: size for the protective device, not just the load; manual entry; icon position

- calculateCableSizing now selects cross-section against
  designCurrentA = max(operatingCurrentA, existingProtectionRatedCurrentA)
  instead of the load current alone. A breaker only trips at its own rated
  current (In), so a cable sized for the actual load could overheat under
  sustained current below that threshold - the standard In <= Iz rule.
  Voltage-drop calculation still uses the real operating current, only the
  capacity check changed. Alerts and the ok-summary now name the breaker as
  the limiting factor when it is one.
- Added a manual cable type/cross-section entry in the modal itself:
  running a calculation pre-fills these fields as a suggestion, but they
  are the single field that actually gets applied, and stay editable -
  this restores the direct manual-entry capability the modal replaced when
  it took over the cableSummary/cableCrossSection cell click.
- Fixed calculator icon position from a trailing ::after (inconsistent
  position depending on cell text length, easy to miss on empty cells) to
  a fixed-position ::before, so it is always in the same place regardless
  of whether cable data is already filled in.
- No new display for the existing protection device - it already has its
  own Schutz column in this app.

src/app/globals.css

@@ -1227,10 +1227,17 @@ a.kpi:hover {
   box-shadow: inset 0 0 0 1px var(--color-primary);
 }
 
-.tree-grid .cell-cable-sizing-trigger::after {
-  content: " 🧮";
+.tree-grid .cell-cable-sizing-trigger {
+  position: relative;
+  padding-left: 1.4em;
+}
+
+.tree-grid .cell-cable-sizing-trigger::before {
+  content: "🧮";
+  position: absolute;
+  left: 0.2em;
   font-size: 0.8em;
-  opacity: 0.7;
+  opacity: 0.8;
 }
 
 .tree-grid .device-drag-handle {