feat(cli): add channel-aware update notifier (#265)

* feat(cli): show cached update notices after commands

* docs(cli): describe update notices

* fix(cli): type update check environment

* fix(cli): decouple update notice display from refresh and harden suppression

Display a cached "update available" notice based solely on the lastNoticeAt
24h throttle, independent of checkedAt refresh freshness, matching the design's
independent display/refresh decisions. Suppress the check unconditionally under
--json, CI, and non-TTY before consulting output-mode preferences, so a
KTX_OUTPUT=pretty override can no longer make CI/non-TTY contexts phone npm.

packages/cli/src/clack.ts

@@ -3,6 +3,30 @@ import type { KtxCliIo } from './cli-runtime.js';
 
 const ESC = String.fromCharCode(0x1b);
 
+export interface CliStyleEnv {
+  NO_COLOR?: string;
+  TERM?: string;
+}
+
+function ansiEnabled(env: CliStyleEnv = process.env): boolean {
+  return !env.NO_COLOR && env.TERM !== 'dumb';
+}
+
+function ansiColor(text: string, open: number, close: number, env?: CliStyleEnv): string {
+  if (!ansiEnabled(env)) {
+    return text;
+  }
+  return `${ESC}[${open}m${text}${ESC}[${close}m`;
+}
+
+export function dim(text: string, env?: CliStyleEnv): string {
+  return ansiColor(text, 2, 22, env);
+}
+
+export function cyan(text: string, env?: CliStyleEnv): string {
+  return ansiColor(text, 36, 39, env);
+}
+
 export interface RailBufferedSource {
   stdoutText(): string;
   stderrText(): string;
@@ -61,11 +85,11 @@ export function createClackSpinner(): KtxCliSpinner {
 }
 
 function magenta(text: string): string {
-  return `${ESC}[35m${text}${ESC}[39m`;
+  return ansiColor(text, 35, 39);
 }
 
 function red(text: string): string {
-  return `${ESC}[31m${text}${ESC}[39m`;
+  return ansiColor(text, 31, 39);
 }
 
 export function createStaticCliSpinner(io: KtxCliSpinnerIo): KtxCliSpinner {