feat: update CSS to include reset and CSS layers

[j-mes]

This pull request introduces a foundational CSS reset to the project and refactors how global styles are organized and loaded. The most significant change is the addition of the Chris Coyier reset stylesheet, which provides a minimal, opinionated baseline for cross-browser consistency. The main stylesheet is updated to use CSS layers for better separation of reset and base styles.

Global CSS organization and reset:

• Added a new src/styles/reset.css file containing the Chris Coyier starting stylesheet, which normalizes browser defaults and establishes consistent base styles for typography, layout, form elements, media, and accessibility.
• Refactored src/styles/index.css to use @layer reset, base and @import "reset.css" within the reset layer, ensuring the reset styles are loaded before custom base styles.

Base style improvements:

• Moved custom base styles (CSS variables, color definitions, etc.) under the @layer base section in src/styles/index.css for clearer separation from the reset styles.

Accessibility and focus handling:

• Ensured the skip link focus-visible style block is properly closed and integrated with the new layered structure.