v10.0.0-beta.6

Beta.6 brings preview thumbnails to the time slider (#935): the default and minimal skins, in both HTML and React, now show a thumbnail of the frame under your pointer as you scrub. The same PR fixes thumbnail state when React connects after the image has already loaded or errored. Two smaller player fixes land alongside it: safe areas around popovers and tooltips (#951) and simpler styles for slotted video in the HTML player (#953).

The docs site gains shiki notation transformers (#937), so code blocks support diff, focus, and word-highlight annotations, with copy buttons that strip the annotation comments. New concept pages cover skins and architecture (#769). Site polish includes restored blank lines in code blocks (#945), better whitespace around links (#913), and a Brightcove typo fix (#915).

Thanks to @esbie for making their first contribution in #917.