Fix flaky anvil-catalog filter deselection test

[Copilot]

The "deselects filters through search bar" test was flaky because selectFirstOption used a positional .first() locator to assert selection state after clicking. When MUI re-sorts the filter list (selected items move position), .first() resolves to a different, unselected element — causing the assertion to fail intermittently.

Changes

• Added namedPopoverFilterItem helper that locates a filter item in the open popover by display name (mirrors the existing namedFilterItem for the autocomplete popper)
• Modified selectFirstOption to use namedPopoverFilterItem for the post-click selection assertion instead of the stale positional locator

// Before: positional locator re-evaluates to wrong element after list re-sort
await option.click();
await expectFilterItemSelected(option); // .first() may now point to a different item

// After: name-based locator is stable regardless of list ordering
await option.click();
await expectFilterItemSelected(namedPopoverFilterItem(page, name));

Known Issues

None.

[frano-m]

LGTM thanks @copilot.