(wip)appview: add copy button

right now, only the textnode inside the button gets added, without the
<button> around it. can't figure out why. the DataAtom and Type match
what html.Parse gives, per https://go.dev/play/p/eW2o3v2eBbY

appview/pages/markup/markdown.go

···
 	"bytes"
 	"fmt"
 	"io"
+	"log"
 	"net/url"
 	"path"
 	"strings"
···
 	"github.com/yuin/goldmark/text"
 	"github.com/yuin/goldmark/util"
 	htmlparse "golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
 
 	"tangled.sh/tangled.sh/core/appview/pages/repoinfo"
 )
···
 					node.Attr[i] = attr
 				}
 			}
+		}
+
+		if node.Data == "pre" {
+			log.Println("found pre yahooooo!!")
+			button := &htmlparse.Node{
+				Type:     htmlparse.ElementNode,
+				DataAtom: atom.Button,
+				Data:     "button",
+				// Attr: []htmlparse.Attribute{
+				// 	{
+				// 		Key: "onclick",
+				// 		Val: "navigator.clipboard.writeText(this.parentElement.parentElement.querySelector('code').innerText)",
+				// 	},
+				// 	{
+				// 		Key: "onload",
+				// 		Val: "this.removeAttribute('aria-hidden')",
+				// 	},
+				// 	{
+				// 		Key: "aria-hidden",
+				// 		Val: "true",
+				// 	},
+				// },
+			}
+
+			button.AppendChild(
+				&htmlparse.Node{
+					Type: htmlparse.TextNode,
+					Data: "Copy",
+				},
+			)
+
+			node.InsertBefore(button, node)
 		}
 
 		for n := node.FirstChild; n != nil; n = n.NextSibling {