feat: rebuild website with SLASHED framework and BEM methodology

- Replaced manual layout with SLASHED primitives (sf-stack, sf-grid, sf-container).
- Adopted BEM naming convention with 'cs-' prefix.
- Encapsulated custom styles in @layer slashed.overrides.
- Fixed Stylelint violations and ensured Conventional Commits compliance.
- Restored accidentally deleted CI test files.
- Optimized performance by using optimal framework bundle from JSDelivr.

Author: jackgranatowski