Refactor frontend to shadcn UI primitives with Tailwind and upgrade React/deps

[andrerfneves]

Motivation

• Replace the app's custom UI and styles with up-to-date shadcn-style UI primitives using Tailwind so the frontend is easier to maintain and reuse.
• Move the codebase to modern React API and upgrade dependency versions to support the new UI primitives and tooling.
• Preserve the exact existing functionality: invoice/LNURL parsing, QR scanning, URL updates and error handling.
• Provide a Tailwind/PostCSS base and utility helpers compatible with shadcn component patterns.

Description

• Converted src/app.js from a class component to a functional component using React hooks and preserved all decode/QR behaviors while plugging in the new UI primitives.
• Added shadcn-style components under src/components/ui/ (button, input, card, dialog, badge, alert) and a cn helper at src/lib/utils.js for class merging.
• Introduced Tailwind and PostCSS configuration and base stylesheet (tailwind.config.js, postcss.config.js, src/index.css) and switched the entry to the React 18 root API in src/index.js.
• Updated package.json to reference updated/new dependencies (Radix, clsx, class-variance-authority, lucide-react, tailwind-merge, Tailwind tooling, and bumped react/react-dom) and changed scripts to use the newer toolchain.

Testing

• Attempted to install dependencies with npm install but it failed due to a 403 Forbidden error from the npm registry, so the install step could not complete.
• No automated tests or builds were successfully executed because dependency installation was blocked by the registry error.
• A Git commit was created with the refactor changes.
• Manual runtime verification was not possible in this environment due to the install error.

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Codex Task

[vercel]

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Project	Deployment	Review	Updated (UTC)
lightning-decoder	Error		Jan 13, 2026 4:31pm