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

bonfire/command.go

@@ -2,12 +2,15 @@ package bonfire
 
 import (
 	"context"
-	"fmt"
-	"io"
+	"errors"
+	"strings"
 
 	"github.com/spf13/cobra"
 )
 
+// ErrCommandName is returned when a plugin command is missing namespace:verb.
+var ErrCommandName = errors.New("bonfire: plugin command name must be namespace:verb")
+
 // Command is a console command value collected from plugins or the tool.
 type Command struct {
 	Name        string
@@ -39,13 +42,6 @@ type Input interface {
 	Flag(name string) (string, bool)
 }
 
-// Output is an injected writer used by commands instead of package-level stdout.
-type Output interface {
-	io.Writer
-	Println(a ...any)
-	Printf(format string, a ...any)
-}
-
 type cobraInput struct {
 	cmd  *cobra.Command
 	spec Command
@@ -84,27 +80,39 @@ func (in cobraInput) Flag(name string) (string, bool) {
 	return val, true
 }
 
-type writerOutput struct {
-	w io.Writer
+func validCommandName(name string) bool {
+	switch name {
+	case "build", "dev":
+		return true
+	}
+	ns, verb, ok := strings.Cut(name, ":")
+	return ok && ns != "" && verb != "" && !strings.Contains(verb, " ")
 }
 
-func (o writerOutput) Write(p []byte) (int, error) {
-	if o.w == nil {
-		return 0, io.ErrClosedPipe
+func commandUsage(c Command) string {
+	parts := []string{c.Name}
+	for _, a := range c.Args {
+		if a.Required {
+			parts = append(parts, "<"+a.Name+">")
+		} else {
+			parts = append(parts, "["+a.Name+"]")
+		}
 	}
-	return o.w.Write(p)
+	return strings.Join(parts, " ")
 }
 
-func (o writerOutput) Println(a ...any) {
-	if o.w == nil {
-		return
+func positionalArgs(args []Arg) cobra.PositionalArgs {
+	required := 0
+	for _, a := range args {
+		if a.Required {
+			required++
+		}
 	}
-	fmt.Fprintln(o.w, a...)
-}
-
-func (o writerOutput) Printf(format string, a ...any) {
-	if o.w == nil {
-		return
+	if required == 0 {
+		return cobra.ArbitraryArgs
 	}
-	fmt.Fprintf(o.w, format, a...)
+	if required == len(args) {
+		return cobra.ExactArgs(required)
+	}
+	return cobra.MinimumNArgs(required)
 }