🐛 Bug: date picker month/year dropdowns inoperable on macOS (native select window blur closes the popover)

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Summary

In the date picker (e.g. work item start/due date) with captionLayout="dropdown", the month/year selectors are native <select> elements. On macOS Chrome, clicking one opens an OS-level dropdown window → the browser window blurs → the surrounding Headless UI Combobox.Options treats it as an outside interaction and instantly closes the whole calendar popover. The selection never lands — the dropdowns look completely inoperable.

Why should this be worked on?

Setting start/due dates is a core workflow; the month/year dropdowns are the only fast way to jump across months (the nav arrows only step one month at a time). On macOS the feature is effectively broken.

Replacing the native <select> with a custom, portal-rendered listbox dropdown (react-day-picker's components.Dropdown override) removes the OS-level popup entirely, so no window blur occurs and the calendar popover stays open. Also fixes the dropdown being clipped by overflow-hidden popover containers.

Working implementation in the linked PR (verified in Storybook with a real browser: month/year menus open, select correctly, calendar grid updates; outside-click/Escape close properly).

Start at the date picker using captionLayout="dropdown" and inspect react-day-picker's components.Dropdown override. Verify the behavior in Storybook with a real browser: month/year menus should open and select correctly, update the calendar grid, remain open on macOS, and close properly on outside click or Escape.