fix: refine earth hud structure and bun startup flow

- refactor the /earth HUD into class-first CSS layers with dedicated base, hud, and toolbar responsibilities
- clean up Earth markup and runtime DOM hooks so shared panel, toolbar, tooltip, and status classes stay consistent after dynamic updates
- keep HUD scaling configurable through extracted constants and remove leftover legacy panel/toolbar styling paths
- make planet.sh self-bootstrap Bun and uv by prepending local runtime bins to PATH and auto-installing missing tools in fresh environments
- document Bun as the frontend package manager of record and sync repository version metadata to 0.24.1

frontend/public/earth/css/coordinates-display.css

@@ -1,42 +1,31 @@
 /* coordinates-display */
 
-#coordinates-display {
-  top: 20px;
-  right: 20px;
-  border-radius: 18px;
-  padding: 10px 15px;
+.hud-panel-coordinates {
+  top: var(--hud-offset);
+  right: var(--hud-offset);
+  border-radius: var(--hud-radius);
+  padding: var(--hud-panel-padding-sm) var(--hud-panel-padding);
   z-index: 10;
-  font-size: 0.9rem;
-  min-width: 180px;
+  font-size: var(--hud-font-size);
+  min-width: calc(180px * var(--hud-scale));
 }
 
-#coordinates-display .coord-item {
-  margin-bottom: 5px;
-  display: flex;
-  justify-content: space-between;
+.hud-panel-coordinates .coord-item {
+  margin-bottom: var(--hud-gap-xs);
 }
 
-#coordinates-display .coord-label {
-  color: #aaa;
-}
-
-#coordinates-display .coord-value {
-  color: #4db8ff;
-  font-weight: 500;
-}
-
-#coordinates-display #zoom-level {
-  margin-top: 5px;
+.hud-panel-coordinates .earth-zoom-level {
+  margin-top: var(--hud-gap-xs);
   color: #ffff44;
   font-weight: 500;
   text-align: center;
-  font-size: 1rem;
+  font-size: calc(1rem * var(--hud-scale));
 }
 
-#coordinates-display .mouse-coords {
-  font-size: 0.8rem;
+.hud-panel-coordinates .earth-mouse-coords {
+  font-size: var(--hud-font-size-sm);
   color: #aaa;
-  margin-top: 5px;
-  padding-top: 5px;
+  margin-top: var(--hud-gap-xs);
+  padding-top: var(--hud-gap-xs);
   border-top: 1px solid rgba(255, 255, 255, 0.1);
 }