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/main.js

@@ -92,7 +92,7 @@ function applyCableVisualState() {
     
     switch (state) {
       case CABLE_STATE.LOCKED:
-        c.material.opacity = 0.3 + pulse * 0.7;
+        c.material.opacity = CABLE_CONFIG.lockedOpacityMin + pulse * (CABLE_CONFIG.lockedOpacityMax - CABLE_CONFIG.lockedOpacityMin);
         c.material.color.setRGB(1, 1, 1);
         break;
       case CABLE_STATE.HOVERED: