How and why did the word tight come to be appropriated in this sense, for example as in, "That car is tight, cuh!" ? I mean, one easily extrapolates from the "normal" definition to understand why slang would appropriate tight to mean "close" — as in "Nah, we cool cuz we tight like that" — but this other sense is significantly opaque to me.
15 Marked by full control over elements or subordinates; firm: tight management; a tight orchestral performance.
In music it usually means all members of an ensemble are playing together with rhythmic and harmonic precision. I think it's not much of a stretch to work from that meaning to the sense of something being remarkable or "slick".
Tight implies being well-designed. If something is designed to physically be tight, everything is held together firmly. Nothing sloppy. So the use of it to describe cool/great/slick is in reference to it being a good design, be it music, cars, a purse, or even relationships (it's good that those two people are together--they fit together well--they "tight").