feat: golang-cli v1.0.0 — generic command-tree CLI library

Reusable, generics-based CLI extracted from vpp-evpn's cmd/evpnc:
a declarative command tree (Node[C]) from which dispatch, '?'-help and
TAB-completion are derived, an interactive Shell[C], dynamic slot
resolvers (context-dependent via captured args), text-or-JSON output
(Emit), and color helpers (Paint/Label/KV). Builds on Linux and OpenBSD
(readline termios override). Includes a self-contained example and a
design proposal under docs/.

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

color.go

@@ -0,0 +1,41 @@
+// SPDX-FileCopyrightText: (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
+// SPDX-License-Identifier: Apache-2.0
+
+package cli
+
+// Bright (high-intensity) ANSI color codes, plus the reset sequence. These are
+// the palette consumed by Paint and Label; status words pop while unremarkable
+// "normal" states can stay uncolored.
+const (
+	Reset  = "\x1b[0m"
+	Red    = "\x1b[91m" // bright red
+	Green  = "\x1b[92m" // bright green
+	Blue   = "\x1b[94m" // bright blue
+	Yellow = "\x1b[93m" // bright yellow
+	Cyan   = "\x1b[96m" // bright cyan
+)
+
+// colorEnabled is process-global, toggled once at startup via SetColor. It
+// defaults to false so output is script-safe unless a program opts in.
+var colorEnabled bool
+
+// SetColor turns colorized output on or off for Paint and Label. Call it once
+// at startup (e.g. from a -color flag): color is useful in an interactive shell
+// but noise when piping one-shot output into scripts.
+func SetColor(on bool) { colorEnabled = on }
+
+// ColorEnabled reports whether colorization is currently on.
+func ColorEnabled() bool { return colorEnabled }
+
+// Paint wraps s in an ANSI color when color is enabled; otherwise it returns s
+// unchanged, so the word still reads in scripts and on no-color terminals.
+func Paint(s, code string) string {
+	if !colorEnabled {
+		return s
+	}
+	return code + s + Reset
+}
+
+// Label wraps s in blue when color is enabled. Use it for static field labels —
+// the "key=" half of a "key=value" pair — so the value stands out in normal font.
+func Label(s string) string { return Paint(s, Blue) }