0.3.0

Added

• Template/layout model — eleven per-slide templates (default, title, section, quote,
  image-focus, two-column, columns-3, stat, cover-image) plus combinable density
  modifiers (compact, code-heavy), chosen with <!-- layout: <template> [modifier…] -->.
  In multi-column layouts the title spans all columns.
• Media that fills and centers — block images and Mermaid diagrams now occupy the available
  space, horizontally and vertically centered and scaled to fit (object-fit: contain), for both
  Obsidian ![[embeds]] and standard ![](…) images — instead of flowing small and left-aligned.
• Deck slots — header:, footer: and paginate: frontmatter render as floating corner
  slots (pagination shows n / N).
• Smart layout inference — with no explicit directive, a lone heading becomes section, a lone
  quote becomes quote, a lone image/diagram becomes image-focus, and <!-- column --> splits
  pick two-column/columns-3; an explicit <!-- layout --> always wins.
• Sparse slides compose vertically — slides with little content are vertically centered instead
  of clinging to the top.
• Per-theme code & Mermaid — a user .css theme can declare its highlight.js and Mermaid theme
  via /* sd-hljs: … */ and /* sd-mermaid: … */ header directives, so dark decks get dark code
  and dark diagrams.

Fixed

• Callout colours now derive from theme tokens, so dark themes render dark callouts without
  per-theme overrides.
• Mermaid diagrams scale to fill their area instead of being capped small.