Clear stale preview inline width when popover becomes alts

When a long-press transforms the preview bubble into the alts listbox,
#openPopover reused the DOM element but only reset className and
children. The inline style.width=anchorWidth from the preview stayed
on the node, so the flex container was pinned at key-width while the
alt buttons laid out their natural sum — they spilled outside the
popover box. #positionPopover now clears the opposite-mode inline
size every time it runs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: chapterjason

src/keyboard/element.ts

@@ -755,7 +755,9 @@ export class VirtualKeyboard extends HTMLElement {
     const anchorRect = anchor.getBoundingClientRect();
     if (popover.classList.contains("preview")) {
       popover.style.width = `${anchorRect.width}px`;
+      popover.style.minWidth = "";
     } else {
+      popover.style.width = "";
       popover.style.minWidth = `${anchorRect.width}px`;
     }