feat(terminal): add dynamic color with NO_COLOR/FORCE_COLOR support

- Convert static ANSI constants to functions for dynamic color control
- Respect NO_COLOR convention (https://no-color.org/)
- Support FORCE_COLOR for CI/CD environments
- setColorEnabled() API for --no-color flag integration

src/terminal.ts

@@ -1,7 +1,35 @@
-export const BOLD = "\x1b[1m";
-export const GREEN = "\x1b[32m";
-export const YELLOW = "\x1b[33m";
-export const CYAN = "\x1b[36m";
-export const RED = "\x1b[31m";
-export const DIM = "\x1b[2m";
-export const RESET = "\x1b[0m";
+// Terminal styling utilities.
+// Respects NO_COLOR convention, --no-color flag, and TTY detection.
+
+import { isStdoutTTY } from "./tty";
+
+let _enabled: boolean | null = null;
+
+export function setColorEnabled(enabled: boolean): void {
+  _enabled = enabled;
+}
+
+export function isColorEnabled(): boolean {
+  if (_enabled !== null) return _enabled;
+
+  // Respect NO_COLOR: https://no-color.org/
+  if (process.env.NO_COLOR !== undefined && process.env.NO_COLOR !== "") {
+    return false;
+  }
+  if (!isStdoutTTY()) return false;
+  if (process.env.FORCE_COLOR && process.env.FORCE_COLOR !== "0") return true;
+
+  return true;
+}
+
+function s(code: string): string {
+  return isColorEnabled() ? code : "";
+}
+
+export const BOLD = () => s("\x1b[1m");
+export const DIM = () => s("\x1b[2m");
+export const GREEN = () => s("\x1b[32m");
+export const YELLOW = () => s("\x1b[33m");
+export const CYAN = () => s("\x1b[36m");
+export const RED = () => s("\x1b[31m");
+export const RESET = () => s("\x1b[0m");