feat: Add animated satellite/signal background to GitHub Pages

Canvas-based animation with orbiting satellite dots, signal pulse rings,
drifting particles, and a faint grid overlay. Uses the accent cyan color
at very low opacity to stay subtle. Particles brighten near the cursor.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/style.css

@@ -17,6 +17,22 @@
     --gradient-end: #0088ff;
 }
 
+/* Animated background canvas */
+#bg-canvas {
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    z-index: 0;
+    pointer-events: none;
+}
+
+body > *:not(#bg-canvas) {
+    position: relative;
+    z-index: 1;
+}
+
 * {
     margin: 0;
     padding: 0;