[UI] Build the "Drag-and-Drop" Upload Component

[mijinummi]

Title: [UI] Build the "Drag-and-Drop" ABI/Spec Upload Component

📝 Description

We need a clean, user-friendly entry point for developers to upload their contract metadata. This component will be the first thing a user sees in the apps/web dashboard.

🎯 Goal

Create a React-based drag-and-drop zone that accepts .json (EVM ABIs) and .wasm (Soroban Specs) files.

✅ Requirements

• Implement a drag-and-drop zone using react-dropzone or native HTML5.
• Add file-type validation to ensure only relevant files are uploaded.
• Provide immediate visual feedback (e.g., a "File Loaded" checkmark) once the file is parsed into memory.