feat: add output package with Formatter interface (#537)

* docs: add RFC-004 for CLI (cobra) and output design
* feat: add output package with Formatter interface and BrowserData.Each
* fix: golangci config array syntax + add output package tests
* refactor: encapsulated Output as Writer, collect-then-write pattern
* refactor: unified row type with reflection-based CSV/JSON output
* fix: ProfileName empty guard, writeFile close error check, sync RFC-004

output/json.go

@@ -0,0 +1,17 @@
+package output
+
+import (
+	"encoding/json"
+	"io"
+)
+
+type jsonFormatter struct{}
+
+func (f *jsonFormatter) ext() string { return "json" }
+
+func (f *jsonFormatter) format(w io.Writer, rows []row) error {
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "  ")
+	enc.SetEscapeHTML(false)
+	return enc.Encode(rows)
+}