Remove x402 demo from repository (#8)

Removes the examples/x402-demo/ directory (frontend, server, simulator),
related docs, and the x402-specific reference in evd doc comments.

Closes #5

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: tac0turtle

bin/evd/src/main.rs

@@ -31,8 +31,8 @@
 //! # Start with default testapp genesis
 //! evd run
 //!
-//! # Start with a custom genesis file (e.g. for x402 demo)
-//! evd run --genesis-file examples/x402-demo/genesis.json
+//! # Start with a custom genesis file
+//! evd run --genesis-file path/to/genesis.json
 //!
 //! # Custom addresses
 //! evd run --grpc-addr 0.0.0.0:50051 --rpc-addr 0.0.0.0:8545