Add hello world example

Minimal Iris application demonstrating:
- Signal creation with NewSignal
- Reactive text rendering with TextFromFunction
- Auto-incrementing counter to show reactivity

Closes #2

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/hello/main.go

@@ -0,0 +1,32 @@
+//go:build js && wasm
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"git.flowmade.one/flowmade-one/iris/reactive"
+	"git.flowmade.one/flowmade-one/iris/ui"
+)
+
+func main() {
+	count := reactive.NewSignal(0)
+
+	// Increment count every second to show reactivity
+	go func() {
+		for {
+			time.Sleep(time.Second)
+			count.Set(count.Get() + 1)
+		}
+	}()
+
+	view := ui.NewView()
+	view.Child(ui.TextFromFunction(func() string {
+		return fmt.Sprintf("Hello, Iris! Count: %d", count.Get())
+	}))
+
+	ui.NewApp(view)
+
+	select {}
+}