cmd/sketch: make browser flag default behavior conditional on one-shot mode

- If the flag is explicitly set (either true or false), respect that choice
- If the flag is not set:
  - In normal mode, default to true (open browser)
  - In one-shot mode, default to false (don't open browser)

This change prevents the browser from opening automatically when in one-shot
mode unless explicitly requested with -open=true.

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/cmd/sketch/main.go b/cmd/sketch/main.go
index 12e58ea..bf0d735 100644
--- a/cmd/sketch/main.go
+++ b/cmd/sketch/main.go
@@ -210,6 +210,19 @@
 	flag.Var(&flags.experimentFlag, "x", "enable experimental features (comma-separated list or repeat flag; use 'list' to show all)")
 
 	flag.Parse()
+
+	// -open's default value should be true normally but false in one-shot mode.
+	// Distinguish between -open default value vs explicitly set.
+	openExplicit := false
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == "open" {
+			openExplicit = true
+		}
+	})
+	if !openExplicit {
+		flags.openBrowser = !flags.oneShot
+	}
+
 	return flags
 }