feat(cli): add no-color output controls

[pengyuayn]

Summary

• Adds a shared color utility that honors both --no-color and the NO_COLOR environment variable.
• Wires the global --no-color option through explain, tx, account, and health output paths.
• Keeps the existing colorize/config exports compatible and documents the color-disable options.
• Removes stale stub code in src/index.ts so the CLI entrypoint typechecks/builds.

Validation

• PASS: npm test -- --run tests/color.test.ts tests/config.test.ts
• PASS: npm run typecheck
• PASS: npm run build

Closes #549