feat(01-03): add deterministic rich CLI output

- Inject bonfire.Output from stdin/stdout/stderr with stdlib widgets and x/term
- Degrade spinner, progress, table and prompts without a TTY or color
- Reject plugin command names that are not namespace:verb

examples/hello/plugins/greeter/plugin_test.go

@@ -3,8 +3,6 @@ package greeter
 import (
 	"bytes"
 	"context"
-	"fmt"
-	"io"
 	"os"
 	"strings"
 	"testing"
@@ -15,17 +13,6 @@ import (
 	"git.golem15.com/golem15/summercms/pact"
 )
 
-type testOut struct{ bytes.Buffer }
-
-func (o *testOut) Write(p []byte) (int, error) { return o.Buffer.Write(p) }
-func (o *testOut) Println(a ...any)            { fmt.Fprintln(&o.Buffer, a...) }
-func (o *testOut) Printf(format string, a ...any) {
-	fmt.Fprintf(&o.Buffer, format, a...)
-}
-
-var _ bonfire.Output = (*testOut)(nil)
-var _ io.Writer = (*testOut)(nil)
-
 type extraMsg struct{ msg string }
 
 func (e extraMsg) Message() string { return e.msg }
@@ -78,9 +65,10 @@ func runHelloCmd(t *testing.T, p *Plugin) string {
 	if len(cmds) == 0 {
 		t.Fatal("no commands")
 	}
-	var out testOut
-	if err := cmds[0].Run(context.Background(), nil, &out); err != nil {
+	var buf bytes.Buffer
+	out := bonfire.NewOutput(strings.NewReader(""), &buf, &buf)
+	if err := cmds[0].Run(context.Background(), nil, out); err != nil {
 		t.Fatalf("Run: %v", err)
 	}
-	return strings.TrimSpace(out.String())
+	return strings.TrimSpace(buf.String())
 }