refactor(maglevc): build the CLI on the golang-cli library

Replace maglevc's hand-rolled command-tree CLI with
git.ipng.ch/ipng/golang-cli v1.3.0, mirroring the evpnc refactor. The
tree (commands.go) and the gRPC-status error unwrap (color.go) stay
app-specific; the generic parts — parse tree, completion, '?'-help, the
readline shell, one-shot dispatch, color helpers, and the watch keypress
handler — now come from the library.

- main.go: a single cli.App[grpcapi.MaglevClient] with a Connect
  callback; drops the flag/color-default/dispatch boilerplate.
- commands.go: `type node = cli.Node[grpcapi.MaglevClient]`; label() ->
  cli.Label(); dyn* gain the captured-args parameter the library's
  Dynamic signature carries; runQuit returns cli.ErrQuit.
- watch.go: keypress.WaitForKey replaces the inline cbreak helper.
- color.go: only formatError remains, reading cli.ColorEnabled().
- delete tree.go, complete.go, shell.go.
- tests use the library API; add TestTreeValid (cli.Validate).

Behavior is unchanged except labels/errors now use the library's bright
ANSI palette (was dark); escape lengths are identical so tabwriter
alignment is unaffected. maglevc additionally gains the OpenBSD readline
fix and BSD-correct watch keypress it previously lacked. Builds on linux
and openbsd.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/client/watch.go

@@ -10,15 +10,15 @@ import (
 	"strconv"
 	"syscall"
 
-	"golang.org/x/sys/unix"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/encoding/protojson"
 
+	"git.ipng.ch/ipng/golang-cli/keypress"
 	"git.ipng.ch/ipng/vpp-maglev/internal/grpcapi"
 )
 
-func dynWatchEventOpts(_ context.Context, _ grpcapi.MaglevClient) []string {
+func dynWatchEventOpts(_ context.Context, _ grpcapi.MaglevClient, _ []string) []string {
 	return []string{"num", "log", "backend", "frontend"}
 }
 
@@ -84,7 +84,7 @@ func runWatchEvents(ctx context.Context, client grpcapi.MaglevClient, args []str
 	watchCtx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	go watchStopOnKeypress(watchCtx, cancel)
+	go keypress.WaitForKey(watchCtx, cancel)
 
 	sigCh := make(chan os.Signal, 1)
 	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
@@ -127,48 +127,5 @@ func runWatchEvents(ctx context.Context, client grpcapi.MaglevClient, args []str
 	}
 }
 
-// watchStopOnKeypress puts stdin into cbreak mode (when it is a terminal) and
-// calls cancel when any byte arrives. Cbreak mode disables canonical (line)
-// input so a single keypress is sufficient, while preserving output
-// post-processing (OPOST/ONLCR) so that fmt.Printf("\n") still produces the
-// expected carriage-return+newline on screen. Falls back gracefully when stdin
-// is not a tty. The goroutine exits when ctx is cancelled.
-func watchStopOnKeypress(ctx context.Context, cancel context.CancelFunc) {
-	fd := int(os.Stdin.Fd())
-	if old, err := stdinCbreak(fd); err == nil {
-		defer unix.IoctlSetTermios(fd, unix.TCSETSF, old) //nolint:errcheck
-	}
-
-	readDone := make(chan struct{})
-	go func() {
-		defer close(readDone)
-		buf := make([]byte, 1)
-		os.Stdin.Read(buf) //nolint:errcheck
-	}()
-
-	select {
-	case <-readDone:
-		cancel()
-	case <-ctx.Done():
-	}
-}
-
-// stdinCbreak sets the terminal referred to by fd into cbreak mode: canonical
-// input and echo are disabled (so single keystrokes are immediately available)
-// but output post-processing is left untouched (so \n still maps to \r\n).
-// Returns the previous termios so the caller can restore it, or an error if fd
-// is not a terminal.
-func stdinCbreak(fd int) (*unix.Termios, error) {
-	old, err := unix.IoctlGetTermios(fd, unix.TCGETS)
-	if err != nil {
-		return nil, err // not a terminal
-	}
-	t := *old
-	t.Lflag &^= unix.ICANON | unix.ECHO | unix.ECHOE | unix.ECHOK | unix.ECHONL
-	t.Cc[unix.VMIN] = 1
-	t.Cc[unix.VTIME] = 0
-	if err := unix.IoctlSetTermios(fd, unix.TCSETS, &t); err != nil {
-		return nil, err
-	}
-	return old, nil
-}
+// Stopping the watch on a keypress now uses keypress.WaitForKey from the
+// golang-cli library (per-platform cbreak handling, with a non-tty fallback).