feat: add README

README.md

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+# LEZ Explorer UI
+
+A Qt6/C++ block explorer for the **Logos Execution Zone** (LEZ). Builds as both a shared library (Qt plugin) and a standalone desktop application.
+
+## Features
+
+- Browse recent blocks with live streaming of new blocks
+- View block details: hash, previous hash, timestamp, status, signature, transactions
+- Navigate to previous blocks via clickable hash links
+- View transaction details (Public, Privacy-Preserving, Program Deployment)
+- View account details with paginated transaction history
+- Full-text search by block ID, block hash, transaction hash, or account ID
+- Browser-style back/forward navigation
+- Pagination with "Load more" for older blocks
+- Dark theme (Catppuccin Mocha)
+
+## Building with Nix
+
+### Standalone application
+
+```sh
+nix build '.#app'
+nix run '.#app'
+```
+
+### Shared library (Qt plugin)
+
+```sh
+nix build '.#lib'
+```
+
+### Development shell
+
+```sh
+nix develop
+```
+
+## License
+
+Licensed under either of
+
+- Apache License, Version 2.0 ([LICENSE-APACHE-v2](LICENSE-APACHE-v2))
+- MIT License ([LICENSE-MIT](LICENSE-MIT))
+
+at your option.