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/layout.go

@@ -0,0 +1,90 @@
+package ui
+
+import "strings"
+
+// VerticalGroup is a view that arranges its children vertically
+// It uses CSS Grid with a single column
+func VerticalGroup(children ...View) View {
+	v := NewView()
+	v.e.Grid()
+	v.e.GridTemplateColumns("1fr") // Force single column
+	v.e.GridAutoFlow("row")
+	v.e.Width("100%")
+	for _, child := range children {
+		v.Child(child)
+	}
+	return v
+}
+
+// HorizontalGroup is a view that arranges its children horizontally
+// It uses flexbox to do so
+func HorizontalGroup(children ...View) View {
+	v := NewView()
+	v.e.Grid()
+	v.e.GridTemplateColumns("repeat(auto-fit, minmax(250px, 1fr))")
+	v.e.Width("100%")
+	for _, child := range children {
+		v.Child(child)
+	}
+	return v
+}
+
+// Spacer is a view that takes up all available space
+// It uses flexbox to do so
+func Spacer() View {
+	v := NewView()
+	v.e.Get("style").Call("setProperty", "flex", "1")
+	return v
+}
+
+// OverlayGroup creates a container where children are stacked on top of each other
+func OverlayGroup(children ...View) View {
+	v := NewView()
+	v.e.Get("style").Call("setProperty", "position", "relative")
+	v.e.Get("style").Call("setProperty", "display", "block")
+
+	// Add children with absolute positioning (except first one)
+	for i, child := range children {
+		if i == 0 {
+			// First child acts as the base layer
+			v.Child(child)
+		} else {
+			// Subsequent children are absolutely positioned as overlays
+			// They need pointer-events: none so clicks pass through to layers below
+			child.e.Get("style").Call("setProperty", "position", "absolute")
+			child.e.Get("style").Call("setProperty", "top", "0")
+			child.e.Get("style").Call("setProperty", "left", "0")
+			child.e.Get("style").Call("setProperty", "width", "100%")
+			child.e.Get("style").Call("setProperty", "height", "100%")
+			child.e.Get("style").Call("setProperty", "pointer-events", "none")
+			v.Child(child)
+		}
+	}
+
+	return v
+}
+
+// Divider creates a visual separator line
+func Divider() View {
+	v := NewView()
+	v.e.Get("style").Call("setProperty", "border-top", "1px solid #ccc")
+	v.e.Get("style").Call("setProperty", "margin", "8px 0")
+	v.e.Get("style").Call("setProperty", "width", "100%")
+	v.e.Get("style").Call("setProperty", "height", "1px")
+	return v
+}
+
+// FlexLayout creates a horizontal layout with explicit column sizing
+// Example: FlexLayout([]string{"48px", "1fr", "240px"}, left, center, right)
+// Supports fixed widths (e.g., "48px"), flexible ("1fr"), and auto-sized ("auto")
+func FlexLayout(columns []string, children ...View) View {
+	v := NewView()
+	v.e.Grid()
+	v.e.Get("style").Call("setProperty", "grid-template-columns", strings.Join(columns, " "))
+	v.e.Width("100%")
+	v.e.Height("100%")
+	for _, child := range children {
+		v.Child(child)
+	}
+	return v
+}