feat: enhance terminal color support and add color profile detection

[brunoantonieto]

my aim here is to fix issue #117, as i believe many mac users (like me) uses the default terminal for any reason to get the job done.

it's not a fancy fix, just asked claude 4 to make a fix based on the comment bellow:

the reason for these styling issues is that we assume in opencode that your terminal supports true color; the built-in mac terminal app only supports ansi 256 color. the recommendation, for now, is to use a more full-featured terminal (i recommend ghostty, it's amazing).

we can leave this issue open until we're able to properly handle a graceful fallback to 256 color. lipgloss supports CompleteColor for defining better fallbacks, but that will only get us part of the way there. we also assume true color in the diff view, and that has some manual escape sequence munging, so we'll need to update that to handle these scenarios as well.