Add screenshot capture tool and dev setup docs

tools/screenshot/main.go

@@ -0,0 +1,41 @@
+// Command screenshot captures a page from the local dev server as a PNG.
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/chromedp/chromedp"
+)
+
+func main() {
+	url := flag.String("url", "http://localhost:8080/directory/", "page to capture")
+	out := flag.String("out", "screenshots/capture.png", "output png path")
+	wait := flag.String("wait", "body", "css selector that must be visible before capturing")
+	flag.Parse()
+	ctx, cancelBrowser := chromedp.NewContext(context.Background())
+	defer cancelBrowser()
+	ctx, cancelTimeout := context.WithTimeout(ctx, 30*time.Second)
+	defer cancelTimeout()
+	var png []byte
+	err := chromedp.Run(ctx,
+		chromedp.EmulateViewport(1280, 800),
+		chromedp.Navigate(*url),
+		chromedp.WaitVisible(*wait, chromedp.ByQuery),
+		chromedp.FullScreenshot(&png, 90),
+	)
+	if err != nil {
+		log.Fatalf("[ERROR] capture %s: %v", *url, err)
+	}
+	if err := os.MkdirAll(filepath.Dir(*out), 0o755); err != nil {
+		log.Fatalf("[ERROR] create output dir: %v", err)
+	}
+	if err := os.WriteFile(*out, png, 0o644); err != nil {
+		log.Fatalf("[ERROR] write %s: %v", *out, err)
+	}
+	log.Printf("captured %s to %s", *url, *out)
+}