MCPay 0.1.0 beta - paid tool execution with signed spend sessions

Closed beta of the MCPay control plane. The repo runs with test ledger credits, no real money moves.

What is inside:

• Signed spend sessions - the gateway accepts only sessions signed by the control plane key, with exact action prices, budget, expiry, and nonce range baked in.
• Distributed claim safety - a nonce is claimed in PostgreSQL before a paid call is dispatched, so two gateway instances cannot charge the same token twice.
• Durable settlement - a delivered 2xx enters the local outbox and settles asynchronously, so a crash between dispatch and response cannot lose a charge.
• Local gateway and browser-based dashboard - run the demo stack and watch sessions settle live.
• TypeScript and Python SDKs - create sessions and poll balances from your agent.
• Test-only ledger credits - wallets top up in demo mode.

Deliberately not in this beta: Stripe deposits, creator payouts, KYC/AML, disputes, and tax workflows.

Run it locally and connect an MCP server: see the README.