feat: add missing file extensions to DEFAULT_INCLUDED_PATTERNS (#119)

Add 19 file extensions from the supported languages table in README.md
that were missing from the default include patterns: Ruby, Swift, Kotlin,
Scala, R, HTML, CSS/SCSS, JSON, XML, YAML, TOML, Solidity, Pascal/Delphi,
DTD, and Fortran.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>