feat(earth): toolbar zoom improvements and toggle-cables

- Remove zoom slider, implement click/hold zoom behavior (+/- buttons)
- Add 10% step on click, 1% continuous on hold
- Add box-sizing/padding normalization to toolbar buttons
- Add toggle-cables functionality with visibility state
- Fix breathing effect: faster pulse (0.008), wider opacity range (0.2-1.0)
- Fix slider null error in updateZoomDisplay
- Set satellite default to hidden

frontend/public/earth/js/cables.js

@@ -11,6 +11,7 @@ export let cableLines = [];
 export let landingPoints = [];
 export let lockedCable = null;
 let cableIdMap = new Map();
+let cablesVisible = true;
 
 function getCableColor(properties) {
   if (properties.color) {
@@ -406,3 +407,17 @@ export function resetLandingPointVisualState() {
     lp.scale.setScalar(1.0);
   });
 }
+
+export function toggleCables(show) {
+  cablesVisible = show;
+  cableLines.forEach(cable => {
+    cable.visible = cablesVisible;
+  });
+  landingPoints.forEach(lp => {
+    lp.visible = cablesVisible;
+  });
+}
+
+export function getShowCables() {
+  return cablesVisible;
+}