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/utils.go

@@ -0,0 +1,10 @@
+//go:build js && wasm
+
+package ui
+
+import "fmt"
+
+// FormatPx formats a float as a CSS pixel value
+func FormatPx(v float64) string {
+	return fmt.Sprintf("%.0fpx", v)
+}