Clicking a chat in the sidebar now processes immediately when using a mouse or
trackpad, but introduces a 300ms delay on touch devices to prevent accidental
navigation when a user scrolls the sidebar and lifts their finger mid-gesture.
Drag is detected when the pointer moves more than 5px from the pointerdown
position; a detected drag cancels any pending tap on release and suppresses
the hover highlight via a .dragging class added synchronously and removed
after a 50ms defer to prevent :hover activating before class removal settles.
The double-tap-to-rename path is unaffected.
Detection uses e.pointerType (already available on the pointerup event) rather
than user-agent sniffing.
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