>> If you use PWM to drive the LEDs you may not need current-
>> limiting resistors. Adjust the duty cycle to suit the supply voltage

> Does this presume the power supply is current limited ?

It IS current-limited. (a) small batteries (b) two semis to get current
through and (c) heat dissipation in the LEDs can be calculated

> What if the supply is not current limited ?

Then you do it another way or limit incoming current. The insistence
seems to be for batteries

> Do the traces provide enough resistance ?  Or is there enough
> inductance to limit current ?

Expecting resistance from traces is futile. AFAIK there is no
useable inductance on the LED side, but you'd probably not want
to be wastefully filtering carefully-generated PWM with inductance
known to be in the way

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