fix: respect FORCE_COLOR level by capping detected terminal capability

[guoyangzhen]

Summary

Fixes #131

When FORCE_COLOR is explicitly set (e.g., FORCE_COLOR=1), the returned color level should be capped at the specified value. Previously, terminal detection would override FORCE_COLOR, making it impossible to reduce color support.

Problem

FORCE_COLOR=1 node -e "console.log(require('chalk').supportsColor)"
# Expected: { level: 1, hasBasic: true, has256: false, has16m: false }
# Actual (in Alacritty/iTerm/etc): { level: 3, hasBasic: true, has256: true, has16m: true }

The issue: forceColor was used as min (floor) but not as cap (ceiling). Terminal capability detection (COLORTERM=truecolor, TERM checks, etc.) would return higher levels without respecting the forced value.

Fix

Add a cap variable set to forceColor when explicitly provided, otherwise Infinity. Apply Math.min(detected_level, cap) at all early return points, ensuring the forced level is never exceeded while still allowing lower detected levels to pass through.

Behavior after fix

• FORCE_COLOR=0 → level 0 (no color)
• FORCE_COLOR=1 → level 1 max (basic 16 colors)
• FORCE_COLOR=2 → level 2 max (256 colors)
• FORCE_COLOR=3 → level 3 (truecolor, same as before)
• No FORCE_COLOR → detected level (same as before)