GitToken Express API Middleware

Express middleware for validating GitHub webhook payloads using GitToken's Ethereum-based token system (v0.2.x). Provides HMAC signature verification with the webhook secret stored on-chain via ERC20 tokens. Key differentiator: integrates blockchain-based authorization directly into webhook handling, enabling token-gated CI/CD pipelines. Compatible with Express 4.x. Not suitable for non-GitHub webhooks or stateless applications. Release cadence: monthly updates.