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>

ui/button.go

@@ -0,0 +1,9 @@
+package ui
+
+import "git.flowmade.one/flowmade-one/iris/internal/element"
+
+func Button(action func(), label View) View {
+	btn := View{element.NewElement("button").On("click", action)}
+	btn.Child(label)
+	return btn
+}