Typography controls and sharper template previews

SlideDrift now includes deck-wide typography controls in the editor's global settings.

You can choose a font pack for a quick visual direction or set heading and body fonts separately. The selected heading font is used for titles and slide hooks, while the body font is used for paragraphs and supporting text.

Generated, shared, previewed, and exported carousels now preserve more authored font choices instead of falling back to the historical defaults. This helps generated decks, remix slides, public share pages, and exports stay closer to the typography you selected.

Template browsing is also more reliable. Template preview images are versioned, stale generated thumbnails are guarded against, and live template previews bypass cached data when needed so template cards and preview modals better match the current template.