feat: add noir, monograph, botanica presets + stacked/typographic/mosaic hero styles + showcase/filmstrip/editorial-flow gallery layouts
- 3 new theme presets: noir (darkroom analog), monograph (typographic book), botanica (organic nature)
- 3 new hero styles: stacked (fullbleed + thumbnail strip), typographic (text-only), mosaic (multi-image grid)
- 3 new gallery layouts: showcase (featured + grid), filmstrip (horizontal scroll), editorial-flow (alternating pairs)
- Extended config types, validation, and CSS tokens for all new options
- Updated theming docs with new presets table, descriptions, and example configs
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