V31: MDX Preview, Ken Burns Video Pan, and PDF Markup Tools

Thirty-one releases. Thirty-one consecutive Fridays. V31 adds an MDX file preview so you can read, search, and edit MDX documents the same way you already do with markdown. The video editor gains an animated horizontal pan -- the Ken Burns effect -- so a still or clip can drift smoothly across the frame, with a replay button and horizontal keyframe chips to fine-tune the motion. PDF text-markup annotation now has its own standalone buttons, so highlighting and marking up a document is a single click instead of a buried menu. The Word editor lets you set table cell border colors with a clean round-trip back to DOCX. Data tables now show a total row count and hide pagination when everything fits on one page. Activity cards show clearer per-phase progress labels. We also refined markdown reading typography and colors for a more comfortable read. On top of that: a fix for missing code syntax highlighting in production builds, video editor playback that now resumes correctly after swapping a clip's source, an image editor that no longer flags false unsaved changes, and clipboard cut that holds its intent when you paste on Mac and Linux.