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/index.html

@@ -39,7 +39,6 @@
     <div id="right-toolbar-group">
       <div id="zoom-toolbar">
         <button id="reset-view" class="zoom-btn">🎯</button>
-        <input type="range" id="zoom-slider" min="0.5" max="5" step="0.01" value="1">
         <button id="zoom-in" class="zoom-btn">+</button>
         <span id="zoom-value" class="zoom-percent">100%</span>
         <button id="zoom-out" class="zoom-btn">−</button>
@@ -48,8 +47,9 @@
       <div id="control-toolbar">
         <div class="toolbar-items">
           <button id="rotate-toggle" class="toolbar-btn" title="自动旋转">🔄<span class="tooltip">自动旋转</span></button>
+          <button id="toggle-cables" class="toolbar-btn active" title="显示/隐藏线缆">🌐<span class="tooltip">隐藏线缆</span></button>
           <button id="toggle-terrain" class="toolbar-btn" title="显示/隐藏地形">⛰️<span class="tooltip">显示/隐藏地形</span></button>
-          <button id="toggle-satellites" class="toolbar-btn" title="显示/隐藏卫星">🛰️<span class="tooltip">显示/隐藏卫星</span></button>
+          <button id="toggle-satellites" class="toolbar-btn" title="显示/隐藏卫星">🛰️<span class="tooltip">显示卫星</span></button>
           <button id="toggle-trails" class="toolbar-btn" title="显示/隐藏轨迹">✨<span class="tooltip">显示/隐藏轨迹</span></button>
           <button id="reload-data" class="toolbar-btn" title="重新加载数据">🔃<span class="tooltip">重新加载数据</span></button>
         </div>