feat: animate fleet of container ships along bay waypoints

Replace the static ship marker with three signal-backed ships that
lerp along waypoint loops through SF Bay (Golden Gate, Oakland, and
Sausalito ferry routes). All clients see the same ship positions via
shared Go state synced every second.

internal/examples/maplibre/main.go

@@ -28,7 +28,7 @@ var (
 
 // shipState tracks a ship lerping along a loop of waypoints.
 type shipState struct {
-	lng, lat  float64
+	lng, lat float64
 	waypoints [][2]float64 // [lng, lat] pairs
 	wpIdx     int          // index of next target waypoint
 	progress  float64      // 0..1 toward next waypoint