Add `--no-color` flag to disable all terminal colors

[kavix]

Description

Currently kurl always outputs with syntax highlighting and colors. Users piping output to files or using terminals without color support need a way to disable colors globally.

Proposed Implementation

kurl https://api.example.com --no-color

Also respect the NO_COLOR environment variable (https://no-color.org/).

Why this matters

Color codes break when piping to less, grep, or saving to files. Standard CLI tools support --no-color or NO_COLOR.

Acceptance Criteria

• Add --no-color CLI flag
• Respect NO_COLOR environment variable
• Disable all ANSI escape codes when flag/env is set
• Works across JSON, HTML, and header output
• Add test coverage

Getting Started

Look at the formatter/color package. The colorization logic likely wraps fmt.Printf or uses a color library. Add a global toggle that returns plain strings when disabled.

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