Add HashProof, Lotero and CompraBTC to Example Apps

[csacanam]

Three live x402 apps in production:

• HashProof (hashproof.dev) — verifiable credentials for $0.10 via x402, USDC on Base or Celo, on-chain + IPFS.
• Lotero (lotero.xyz) — provably fair slot machine, 1.1 USDC spins via x402 on Base with Chainlink VRF.
• CompraBTC (comprabtc.vercel.app) — non-custodial Bitcoin DCA on Celo with a permissionless x402-payable execution endpoint.

All three also ship MCP servers (official registry) and agent skills.

🤖 Generated with Claude Code