Add drawPng function to Renderer for PNG icon rendering

- Takes image.Image, position (x,y) in Dp, size (width,height) in Dp
- Tint color with alpha < 255 applies color overlay using clip.Rect
- Converts Dp to pixels using Renderer.toPx()
- Uses paint.NewImageOp for image rendering

internal/ui/render.go

@@ -369,3 +369,35 @@ type WindowConstraints struct {
 	Min image.Point
 	Max image.Point
 }
+
+// drawPng draws a PNG image at the given position and size.
+// x, y are in Dp (top-left corner).
+// width, height are in Dp (target size).
+// col is the tint color — if alpha < 255, the image is tinted using blendOp.DstIn.
+func (r *Renderer) drawPng(gtx layout.Context, img image.Image, x, y Dp, width, height Dp, col color.NRGBA) {
+	if img == nil {
+		return
+	}
+
+	// Convert Dp to pixels
+	xPx := int(r.toPx(x))
+	yPx := int(r.toPx(y))
+	wPx := int(r.toPx(width))
+	hPx := int(r.toPx(height))
+
+	// Compute destination rectangle
+	dst := image.Rect(xPx, yPx, xPx+wPx, yPx+hPx)
+
+	// If tint color has alpha < 255, apply tint using blendOp.DstIn
+	if col.A < 255 {
+		// Draw tinted rectangle over the image
+		bgClip := clip.Rect(dst).Push(gtx.Ops)
+		paint.ColorOp{Color: col}.Add(gtx.Ops)
+		paint.PaintOp{}.Add(gtx.Ops)
+		bgClip.Pop()
+	}
+
+	// Draw the image
+	paint.NewImageOp(img).Add(gtx.Ops)
+	paint.PaintOp{}.Add(gtx.Ops)
+}