Style closed issues differently in issue list output

Context

tangled issue list currently shows open and closed issues with identical formatting, distinguished only by the [OPEN] / [CLOSED] text label. As the issue list grows (especially once --state all is supported, issue #15), closed issues become visual noise that competes with open ones.

The gh CLI uses colour and dimming to make closed/merged items visually recede, which helps users quickly scan for actionable items at a glance.

Tasks

• Apply distinct styling to closed issues in tangled issue list output — for example, dim/grey text or a different colour for the [CLOSED] badge and title.
• Use a terminal colour library already in the project (or add a lightweight one such as kleur or chalk) to apply the styling.
• Ensure styling is suppressed when stdout is not a TTY (piped output should remain plain text) — consistent with the "TTY = human mode, pipe = machine mode" philosophy in the README.
• Add or update tests to verify that ANSI codes are present in TTY mode and absent in non-TTY mode for closed issues.

Notes

Colour output should only be applied when process.stdout.isTTY is true, to keep piped and --json output clean. This is a display-only change with no effect on data or API calls.