feat: refactor maplibre for reactive signals and Via-native API

- Export Signal type (signal → Signal) so subpackages can reference it
- Expose viewport signals as public fields (CenterLng, CenterLat, Zoom,
  Bearing, Pitch) for .Text() display and .Bind() usage
- Add signal-backed marker positions (LngSignal/LatSignal) with
  data-effect reactivity for server push and dragend writeback
- Add event system (MapEvent, OnClick, OnLayerClick, OnMouseMove,
  OnContextMenu) using hidden inputs + action triggers
- Add Source interface replacing type-switch, with RawSource escape hatch
- Add CameraOptions for FlyTo/EaseTo/JumpTo/FitBounds/Stop
- Add Control interface with NavigationControl, ScaleControl,
  GeolocateControl, FullscreenControl
- Expand Options with interaction toggles, MaxBounds, and Extra map
- Add effectspike example to validate data-effect with server-pushed signals
- Update maplibre example to showcase all new features

actiontrigger.go

@@ -97,7 +97,7 @@ func buildAttrKey(event string, opts *triggerOpts) string {
 }
 
 // WithSignal sets a signal value before triggering the action.
-func WithSignal(sig *signal, value string) ActionTriggerOption {
+func WithSignal(sig *Signal, value string) ActionTriggerOption {
 	return withSignalOpt{
 		signalID: sig.ID(),
 		value:    fmt.Sprintf("'%s'", value),
@@ -105,7 +105,7 @@ func WithSignal(sig *signal, value string) ActionTriggerOption {
 }
 
 // WithSignalInt sets a signal to an int value before triggering the action.
-func WithSignalInt(sig *signal, value int) ActionTriggerOption {
+func WithSignalInt(sig *Signal, value int) ActionTriggerOption {
 	return withSignalOpt{
 		signalID: sig.ID(),
 		value:    strconv.Itoa(value),