feat: add Prettier for consistent code formatting

[Ai-chan-0411]

Summary

Adds Prettier configuration for consistent code formatting across the project:

• .prettierrc with sensible defaults (2-space indent, semicolons, double quotes, trailing commas)
• Includes prettier-plugin-tailwindcss for automatic Tailwind class sorting
• .prettierignore to skip build artifacts and lock files
• format and format:check npm scripts for easy usage

Closes #27

Test Plan

• Run pnpm install to install Prettier
• Run pnpm format:check to verify config is picked up
• Run pnpm format to format the codebase

[vercel]

@aoi-dev-0411 is attempting to deploy a commit to the osama's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Thank you for the pull request! ✅

A maintainer will review this soon. Please be patient while we take a look. 🙌

[Ai-chan-0411]

Closing this PR as there has been no maintainer feedback for several weeks. Thank you for the opportunity to contribute! Feel free to reopen if you would like these changes.