feat: add --color=auto|always|never

[nfvelten]

Closes #121.

Color was decided only by the isatty and NO_COLOR checks. --no-fancy could force it off, but nothing could force it on, so piping into anything else always stripped it. That is the case in the issue: the output is captured into a variable and reused for a notification border, the terminal, and the clipboard.

--color follows the ls convention. auto is the default and behaves exactly as before, always keeps the color across a pipe, and never is what --no-fancy already did. --no-fancy now routes through the same tri-state rather than setting the flag directly, so the last option on the command line wins instead of the order of the checks deciding.

Verified by picking a pixel with the output piped through cat -v:

$ hyprpicker | cat -v
#FAF0C6

$ hyprpicker --color=always | cat -v
^[[38;2;0;0;0;48;2;250;240;198m#FAF0C6^[[0m

An unrecognised value exits 1 with a message naming the three accepted ones.

Two notes, both easy to drop if you disagree:

• the man page documented --no-fancy as -n, but -n is --notify and --no-fancy is -b. I corrected it in the same block I was already editing.
• the NO_COLOR entry now says it is overridden by --color=always, matching how ls treats an explicit flag.

While looking into this I also noticed #109 is already fixed, by #123 back in May 2025. The preview honours --format on current main. Might be worth closing.

[github-actions]

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