The single-row chip strip relied on native horizontal scroll, which is
hard to reach without a horizontal wheel. Wire two scroll mechanisms
on the strip once it's rendered:
- Vertical wheel → horizontal scroll (intercept only when overflow
exists and the wheel motion is primarily vertical, so normal page
scroll still works elsewhere).
- Mouse grab-and-drag: cursor goes grab/grabbing, mousedown→move
bumps scrollLeft by the cursor delta. A 5px drag threshold cancels
the chip click so the user can drag-scroll without accidentally
switching accounts.
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