what

The @tamagui/to-tailwind converter emitted a dangling border- class for
borderWidth={1} (Tailwind's border = 1px). Root cause: transform.ts
propValueToClass joins ${prefix}-${tailwindValue}, and the 1px case returns
an empty tailwindValue, producing border- instead of the bare border.

reproduction (before)

<View borderWidth={1} />                          => className="border-"
<View borderWidth={1} borderColor="$borderColor" /> => className="border- border-borderColor"

after

<View borderWidth={1} />                          => className="border"
<View borderWidth={1} borderColor="$borderColor" /> => className="border border-borderColor"
<View borderWidth={2} />                          => className="border-2"   (unchanged)

fix

When tailwindValue is empty, emit the bare prefix (the prefix itself is the
class) instead of ${prefix}-.

proof

• Added a regression test asserting border border-borderColor and no dangling
  border-.
• @tamagui/to-tailwind test:web: 40/40 pass.

context

Surfaced while converting Soot's templates/app to Tailwind against the v3
beta: across all 70 template .tsx, this was the sole source of dangling
classes; with the fix, the bulk codemod produces zero dangling classes.