“Stripes” gradient preset output is missing hint values

The stripes sample is rendering solid black.

Generated output:

```
:root {
--hdr-gradient: linear-gradient(
to top right in oklab,
#fff, #000 0%, #fff 0%, #000 0%, #fff 0%, #000 0%
);
--sdr-gradient: linear-gradient(to top right, #fff, #000 0%, #fff 0%, #000 0%, #fff 0%, #000 0%);

background: var(--hdr-gradient);
}
```
If I nudge the % values in the UI the values are inserted. e.g.

```
:root {
--hdr-gradient: linear-gradient(
to top right in oklab,
#fff, 11%, #000 0% 21%, 31%, #fff 0% 41%, 51%, #000 0% 61%, 71%, #fff 0% 81%, 91%, #000 0% 99%
);
--sdr-gradient: linear-gradient(to top right, #fff, 11%, #000 0% 21%, 31%, #fff 0% 41%, 51%, #000 0% 61%, 71%, #fff 0% 81%, 91%, #000 0% 99%);

background: var(--hdr-gradient);
```

Same in Firefox (146.0b3) and a webkit browser (Orion).

Reproduce the “Stripes” preset in the UI and compare its generated CSS with the output after nudging the percentage values. Trace where the preset’s gradient stops are generated; done means the preset emits its hint values instead of repeated 0% values and renders stripes in Firefox and a WebKit browser.

Written by the indexing model from the issue text.