feat: add react-tailwind-fast template powered by UnoCSS for instant browser execution

[MiltonAkash]

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PR Title

feat: add react-tailwind-fast template powered by UnoCSS for instant browser execution

PR Description

What does this PR do?
This PR introduces a new react-tailwind-fast template that brings instantaneous, client-side Hot Module Replacement (HMR) to React + Tailwind projects within CodeSandbox.

Why is this needed?
Historically, standard React + Tailwind templates (like react-tailwind) rely on Vite and PostCSS plugins. Because the lightweight CodeSandbox in-browser bundler does not natively support those back-end plugins, those templates are forced to boot up as Devboxes (server VMs), resulting in noticeable boot-up delays and network latency during refreshes.

To solve this, this new template utilizes UnoCSS (@unocss/preset-uno). UnoCSS functions natively as a drop-in replacement for Tailwind that is compatible with the CodeSandbox browser environment, allowing users to write standard Tailwind utility classes while enjoying the blazing-fast speeds of a client-side sandbox.

Key Changes:

• Template Scaffolding: Duplicated the standard react-vite-ts template into a new react-tailwind-fast workspace.
• UnoCSS Integration: Initialized UnoCSS inside vite.config.ts, created a uno.config.ts configuration file, and injected virtual:uno.css into the React entry point (main.tsx).
• Demonstration: Replaced the generic App.tsx styles with actual Tailwind utility classes (e.g., flex, bg-gradient-to-r, hover:opacity-80) to showcase immediate out-of-the-box compatibility.
• Documentation: Rewrote the README.md to explicitly educate users on why UnoCSS is used in this template to bypass server Devbox latency.
• Registry Update: Registered the new configuration securely inside the core templates.json list and updated .codesandbox/template.json.

[codesandbox]

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