fix(toolbar): Center icons in the toolbar buttons

Only `a.cesium-toolbar-button` was flex-centered, so the `<button>`
variants let their icons drift: Nuxt UI renders icons as block-level
SVGs that hug the button's left edge, and the custom background icons
leaned on manual margin nudges. Flex-center every app toolbar button
(scoped to #toolbarLeft / #toolbarRight so Cesium's own buttons stay
untouched) and drop the now-redundant margin hacks. All toolbar icons
now sit dead-centered.

Assisted-by: ClaudeCode:claude-opus-4-8

Author: Flowm

src/css/main.css

@@ -100,7 +100,11 @@ input:checked + .slider::before {
   color: #ffffff;
 }
 
-a.cesium-toolbar-button {
+/* Center the icon (custom <i> background icons or Nuxt UI <svg>) in every
+   app toolbar button. Applies to both <a> and <button>; without flex the
+   block-level Iconify SVGs hug the button's left edge. */
+#toolbarLeft .cesium-toolbar-button,
+#toolbarRight .cesium-toolbar-button {
   align-items: center;
   justify-content: center;
   display: inline-flex;
@@ -117,12 +121,9 @@ a.cesium-toolbar-button {
   background: url("../images/icons/sat/2.svg") no-repeat;
   filter: brightness(3.1);
   transform: rotate(-90deg);
-  margin-bottom: 2px;
 }
 
 .svg-groundstation {
   background: url("../images/icons/sat/9.svg") no-repeat;
   filter: brightness(3.1);
-  margin-bottom: 2px;
-  margin-left: 2px;
 }