fix(webapp): drop the shadow from the tertiary slider handle

The run timeline's zoom handle carried a 4px-spread drop shadow that read
as a dark halo. Removed from the variant rather than the call site, so the
storybook sample matches.

The `focus:` copy of the shadow went with it: it was byte-identical to the
base one, so focus already looked the same as rest and nothing is lost.
Also drops `hover:border-text-dimmed`, which set the border to the colour
it already was.

Author: samejr

apps/webapp/app/components/primitives/Slider.tsx

@@ -26,8 +26,7 @@ const variants = {
     root: "h-4",
     track: "h-1 bg-grid-bright group-hover:bg-background-dimmed",
     range: "bg-transparent group-hover:bg-secondary",
-    thumb:
-      "h-3 w-3 border-2 border-text-dimmed bg-grid-bright shadow-[0_1px_3px_4px_rgb(0_0_0/0.2),0_1px_2px_-1px_rgb(0_0_0/0.1)] hover:border-text-dimmed focus:shadow-[0_1px_3px_4px_rgb(0_0_0/0.2),0_1px_2px_-1px_rgb(0_0_0/0.1)]",
+    thumb: "h-3 w-3 border-2 border-text-dimmed bg-grid-bright",
     thumbSize: 12,
     mark: "bg-grid-bright border-background-dimmed",
     markHover: "hover:bg-text-dimmed",