Initial iris repository structure

WASM reactive UI framework for Go:
- reactive/ - Signal[T], Effect, Runtime
- ui/ - Button, Text, Input, View, Canvas, SVG components
- navigation/ - Router, guards, history management
- auth/ - OIDC client for WASM applications
- host/ - Static file server

Extracted from arcadia as open-source component.

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

reactive/signal.go

@@ -0,0 +1,52 @@
+package reactive
+
+type SignalId int
+
+type Signal[T any] struct {
+	*Runtime
+	SignalId
+}
+
+func NewSignal[T any](initial T) Signal[T] {
+	rt := GetRuntime()
+	id := SignalId(len(rt.signalValues))
+	rt.signalValues = append(rt.signalValues, initial)
+	return Signal[T]{rt, id}
+}
+
+func NewSignalWithRuntime[T any](rt *Runtime, initial T) Signal[T] {
+	id := SignalId(len(rt.signalValues))
+	rt.signalValues = append(rt.signalValues, initial)
+	return Signal[T]{rt, id}
+}
+
+func (s *Signal[T]) Get() T {
+	val := s.Runtime.signalValues[s.SignalId]
+
+	if rt := s.Runtime; rt.runningEffect != nil {
+		// Check if this effect is already subscribed to this signal
+		subscribers := rt.signalSubscribers[s.SignalId]
+		alreadySubscribed := false
+		for _, effectId := range subscribers {
+			if effectId == *rt.runningEffect {
+				alreadySubscribed = true
+				break
+			}
+		}
+		if !alreadySubscribed {
+			rt.signalSubscribers[s.SignalId] = append(rt.signalSubscribers[s.SignalId], *rt.runningEffect)
+		}
+	}
+
+	return val.(T)
+}
+
+func (s *Signal[T]) Set(v T) {
+	s.Runtime.signalValues[s.SignalId] = v
+
+	if subscribers, ok := s.Runtime.signalSubscribers[s.SignalId]; ok {
+		for _, effectId := range subscribers {
+			runEffect(s.Runtime, effectId)
+		}
+	}
+}