* Fix clipped card shadows in Hub trending carousel
The carousel scroller only had vertical padding, so with overflow-x set
the first and last cards had their drop shadow clipped on the horizontal
edges. Add px-2 with a matching -mx-2 so the shadow has room while the
cards stay aligned with the section heading, and scroll-px-2 so snap-start
does not scroll the padding away on load.
* Align carousel edge fades with the scroll clip edge
The shadow fix gave the scroller an -mx-2 bleed, but the left/right fade
overlays stayed pinned to the wrapper edges, 8px inside the clip edge. That
left a thin strip where a card showed beside the fade, so the fade read as a
separate block instead of blending into the background. Offset both fades by
the same 8px so their opaque edge sits on the clip edge.
* Add click-and-drag panning to the Hub card carousel
The rows only scrolled by wheel or trackpad, and grabbing a card started
a native drag of its avatar image, so the cards could not be dragged to
move the row. Add mouse drag-to-scroll (touch and pen keep native
scrolling), swallow the click a drag would otherwise fire on a card, keep
plain clicks working, and block the avatar's native drag.
* Trim carousel edge fade width from 56px to 44px
* Smooth out carousel drag panning
Scroll snap was correcting the position on every drag frame, which made
the pan feel sticky. Disable snap while a drag is active and restore it on
release so the row follows the pointer and then settles on a card.
* Drop stale carousel drag when the button is released off-element
If a press ended outside the scroller before the drag threshold was
crossed, no pointerup reached us and the drag stayed armed, so a later
buttonless mousemove would scroll the row. Bail out and clear the drag
whenever the primary button is no longer held.
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