fix(elements): keep branch switching with consumer className

[ephraimduncan]

Passing any className to MessageBranchContent made every branch render at once, so the Previous/Next controls stopped producing a visible change. The consumer class sat in the props spread after the component's computed className, replacing the hidden/block state classes entirely. Even without a consumer class, tailwind-merge collapsed the conflicting grid/block utilities to block, so the active branch never got its intended grid layout.

The wrapper now derives display from a single state-dependent utility (grid when active, hidden otherwise) placed after the consumer class in cn(), so branch visibility always wins the merge while consumer classes still extend the wrapper. Trade-off: a consumer can no longer override the active branch's display type.

Regression test renders two branches with className="rounded-md" and asserts exactly one wrapper is grid before and after clicking Next; full message suite passes 31/31 in Chromium.

[vercel]

@ephraimduncan is attempting to deploy a commit to the Vercel Team on Vercel.

A member of the Team first needs to authorize it.