🚀 Feat: improve the feedbacks with toas instead of banners

[NicolaLC]

This PR introduces several improvements:
closes: #19

• Adds Tailwind v4
• Add shadcn button and sonner components
• Add Storybook
• Add bun.lock

[Copilot]

Pull Request Overview

This PR introduces toast notifications using Sonner, adds Tailwind CSS v4 support, integrates shadcn UI components (button and sonner), and sets up Storybook for component development.

Key Changes

• Replaced Primer React Flash components with Sonner toast notifications across all pages
• Added Tailwind CSS v4 with custom theme configuration
• Integrated shadcn button and sonner components
• Set up Storybook for UI component documentation and testing

Reviewed Changes

Copilot reviewed 19 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
frontend/package.json	Added new dependencies: tailwindcss, sonner, next-themes, lucide-react, storybook and related packages
frontend/yarn.lock	Lock file updates for all new dependencies
frontend/vite.config.ts	Added Tailwind CSS Vite plugin and path aliases configuration
frontend/tsconfig.json	Added path alias configuration for @/* imports
frontend/index.css	New Tailwind CSS v4 configuration with custom theme variables
frontend/src/main.tsx	Import new CSS file
frontend/src/components/ui/sonner.tsx	New Toaster component using Sonner with custom styling
frontend/src/components/ui/button.tsx	New shadcn button component with variants
frontend/src/pages/*.tsx	Refactored to use toast notifications instead of Flash components
frontend/.storybook/*	Storybook configuration files
frontend/components.json	Shadcn UI configuration

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[nicofretti]

The PR is now ready to merge, GG @NicolaLC