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

signal.go

@@ -9,27 +9,27 @@ import (
 )
 
 // Signal represents a value that is reactive in the browser. Signals
-// are synct with the server right before an action triggers.
+// are synced with the server right before an action triggers.
 //
 // Use Bind() to connect a signal to an input and Text() to display it
 // reactively on an html element.
-type signal struct {
+type Signal struct {
 	id      string
 	val     any
 	changed bool
 	err     error
 }
 
-// ID returns the signal ID
-func (s *signal) ID() string {
+// ID returns the signal ID.
+func (s *Signal) ID() string {
 	return s.id
 }
 
 // Err returns a signal error or nil if it contains no error.
 //
 // It is useful to check for errors after updating signals with
-// dinamic values.
-func (s *signal) Err() error {
+// dynamic values.
+func (s *Signal) Err() error {
 	return s.err
 }
 
@@ -39,7 +39,7 @@ func (s *signal) Err() error {
 // Example:
 //
 //	h.Input(h.Type("number"), mysignal.Bind())
-func (s *signal) Bind() h.H {
+func (s *Signal) Bind() h.H {
 	return h.Data("bind", s.id)
 }
 
@@ -48,33 +48,33 @@ func (s *signal) Bind() h.H {
 // Example:
 //
 //	h.Div(mysignal.Text())
-func (s *signal) Text() h.H {
+func (s *Signal) Text() h.H {
 	return h.Span(h.Data("text", "$"+s.id))
 }
 
 // SetValue updates the signal’s value and marks it for synchronization with the browser.
 // The change will be propagated to the browser using *Context.Sync() or *Context.SyncSignals().
-func (s *signal) SetValue(v any) {
+func (s *Signal) SetValue(v any) {
 	s.val = v
 	s.changed = true
 	s.err = nil
 }
 
-// String return the signal value as a string.
-func (s *signal) String() string {
+// String returns the signal value as a string.
+func (s *Signal) String() string {
 	return fmt.Sprintf("%v", s.val)
 }
 
 // Bool tries to read the signal value as a bool.
 // Returns the value or false on failure.
-func (s *signal) Bool() bool {
+func (s *Signal) Bool() bool {
 	val := strings.ToLower(s.String())
 	return val == "true" || val == "1" || val == "yes" || val == "on"
 }
 
 // Int tries to read the signal value as an int.
 // Returns the value or 0 on failure.
-func (s *signal) Int() int {
+func (s *Signal) Int() int {
 	if n, err := strconv.Atoi(s.String()); err == nil {
 		return n
 	}