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/effect.go

@@ -0,0 +1,18 @@
+package reactive
+
+type EffectId int
+
+func NewEffect(f func()) {
+	rt := GetRuntime()
+	effectId := EffectId(len(rt.effects))
+	rt.effects = append(rt.effects, f)
+
+	runEffect(rt, effectId)
+}
+
+func NewEffectWithRuntime(rt *Runtime, f func()) {
+	effectId := EffectId(len(rt.effects))
+	rt.effects = append(rt.effects, f)
+
+	runEffect(rt, effectId)
+}