fix(chrome): clear storage over cdp instead of scripting an opaque origin

Launch runs while the tab is still on about:blank, whose opaque origin denies
storage access, so localStorage.clear() threw SecurityError and every web run
died at launch. Storage.clearDataForOrigin needs no navigation. The exception
helper lands here because "Uncaught" is what hid this for so long.

Claude-Session: https://claude.ai/code/session_01Fj4wJUikdABuMQEETwW55J

internal/driver/chrome/launch_test.go

@@ -0,0 +1,47 @@
+package chrome
+
+import (
+	"testing"
+
+	"github.com/chromedp/cdproto/runtime"
+)
+
+func TestSecurityOrigin(t *testing.T) {
+	cases := map[string]string{
+		"http://localhost:8088":           "http://localhost:8088",
+		"http://localhost:5173/":          "http://localhost:5173",
+		"https://app.example.com/a/b?c=d": "https://app.example.com",
+		"data:text/html,<body>hi</body>":  "",
+		"file:///tmp/index.html":          "",
+		"about:blank":                     "",
+		"":                                "",
+		"://not a url":                    "",
+	}
+	for target, want := range cases {
+		if got := securityOrigin(target); got != want {
+			t.Errorf("securityOrigin(%q) = %q, want %q", target, got, want)
+		}
+	}
+}
+
+// TestExceptionMessage_PrefersDescription pins the useful half of a page
+// exception. ExceptionDetails.Text is "Uncaught" for every throw; the
+// description is where the error a caller can act on lives.
+func TestExceptionMessage_PrefersDescription(t *testing.T) {
+	withDescription := &runtime.ExceptionDetails{
+		Text: "Uncaught",
+		Exception: &runtime.RemoteObject{
+			Description: "SecurityError: Access is denied for this document.",
+		},
+	}
+	if got := exceptionMessage(withDescription); got != withDescription.Exception.Description {
+		t.Errorf("exceptionMessage = %q, want the description", got)
+	}
+	textOnly := &runtime.ExceptionDetails{Text: "Uncaught SyntaxError"}
+	if got := exceptionMessage(textOnly); got != "Uncaught SyntaxError" {
+		t.Errorf("exceptionMessage = %q, want the text fallback", got)
+	}
+	if got := exceptionMessage(nil); got != "" {
+		t.Errorf("exceptionMessage(nil) = %q, want empty", got)
+	}
+}