feat: import all remaining shortcodes from previous theme

feat: import all remaining shortcodes from previous theme

Added 11 additional shortcodes with complete documentation:

Text formatting:
- strike: strikethrough text
- em: highlighted/marked text
- dropcap: paragraph with decorative drop cap

Container wrappers:
- div / div-close: semantic div containers with classes

Gallery:
- gallery: gallery container
- gal-img: gallery images (400px WebP thumbnail with link)

Utility:
- svg: inline SVG icons from assets/SVGs/
- actions: button-style action links
- search: search form with results display
- contact: comprehensive contact form

All shortcodes now fully documented in CONTENT_GUIDE with usage examples and parameters.

Co-Authored-By: Claude Haiku 4.5 <redacted>