Fix set_target matrix format: send 4x4 nested array

The backend expects np.array() to produce a 4x4 matrix, so we need
to send nested arrays instead of a flat 16-element array.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.html

@@ -664,11 +664,12 @@
             const cy = Math.cos(yawRad), sy = Math.sin(yawRad);
             const cp = Math.cos(pitchRad), sp = Math.sin(pitchRad);
 
+            // 4x4 transformation matrix (nested array for numpy compatibility)
             const matrix = [
-                cy * cp, -sy, cy * sp, 0,
-                sy * cp,  cy, sy * sp, 0,
-                -sp,       0,      cp, 0,
-                0,         0,       0, 1
+                [cy * cp, -sy, cy * sp, 0],
+                [sy * cp,  cy, sy * sp, 0],
+                [-sp,       0,      cp, 0],
+                [0,         0,       0, 1]
             ];
 
             dataChannel.send(JSON.stringify({ set_target: matrix }));