)

## Problem

When `flip: true` is set on a brace, the brace is drawn pointing in the
opposite direction, but the `spike` and `content` anchors were always
positioned using positive amplitude values. This caused labels to appear
on the wrong side of flipped braces.

## Solution

This fix multiplies both `amplitude` and `content-offset` by -1 when
`flip` is true, ensuring anchors are positioned correctly on both normal
and flipped braces.

## Related Issues

This is similar to the fix for `flat-brace` in PR #688, but applies to
the regular `brace` function which was not included in that fix.

## Testing

Tested with both horizontal and diagonal braces, with and without flip.
Labels now correctly position on the appropriate side of the brace in
all cases.