Add Prettier configuration

[blakehimeno]

Adds Prettier for automatic code formatting across the project.

• Installed prettier and prettier-plugin-astro as dev dependencies
• Created .prettierrc with standard formatting rules and Astro plugin configuration
• Created .prettierignore to exclude node_modules, dist, build, and .astro folders
• Added format and format:check scripts to package.json
• Ran npm run format to apply initial formatting to existing files