show hover cursor in the PR animation

[vvo]

tl;dr; makes the PR animation read as a hover demo by adding a cursor and stopping after one playback.

Problem

• The GIF looks like the PR title scrolls automatically forever.

Solution

• We show a mouse cursor over the linked title.
• The GIF pauses, plays one marquee cycle, then stops at rest.

Implementation details

• Both light and dark GIFs use the same cursor position and timing.
• The GIF loop count is one.