v0.26.0

• Added raw data decryption and CLI piping support via
  ComplexConfig::Provider#decrypt_data.
• Enhanced the complex_config CLI with a -k flag for explicit key file
  paths and a -I flag for streaming decryption from stdin to stdout.
• Renamed ComplexConfig::Settings#attributes_update_if_nil to
  ComplexConfig::Settings#attributes_update_if_undefined to correctly
  preserve existing keys, including explicit nil overrides; added a
  deprecation layer for the old method.
• Hardened the encryption CLI by replacing Tempfile.open with
  Tempfile.create and adding .yml suffixes to temporary files for improved
  editor syntax highlighting.
• Expanded README.md with guides on secure secret comparison using process
  substitution, automation via input redirection, and critical security
  warnings regarding plain-text secrets in version control.
• Introduced a GitHub Actions workflow for automated documentation deployment
  to GitHub Pages.