fix(ui5-calendar): set timestamp of daypicker on mousedown

[hinzzx]

Overview

Clicking a day in ui5-calendar / ui5-date-picker could move focus to the wrong day.

The root cause

_safelySetTimestamp (which determines the focused date) was only called during the click event, but onAfterRendering fires a focus() call triggered by the preceding mousedown, before click - so focus landed on the previously focused day instead of the clicked one.

What We Did

• In the day picker, that is a composite component of the calendar, we now set the timestamp on mousedown

What This Fixes

• Clicking a day now moves focus to that day immediately, even when onAfterRendering fires focus() before the click event resolves

Fixes: #12914

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13527--ui5-webcomponents-preview.netlify.app

[GDamyanov]

Could we also add test?

[nnaydenow]

Screen.Recording.2026-05-15.at.10.59.46.mov

[hinzzx]

Screen.Recording.2026-05-15.at.10.59.46.mov

Fixed.

[GDamyanov]

LGTM