[Enhancement] Tipping notarization uses randomBytes mock txHash instead of a real blockchain transaction #767

Overview

src/app/api/tipping/route.ts generates the transaction hash using randomBytes(16).toString('hex') with senderAddress: 'anonymous' and chainId: 'server'. The notarization proof is a hash of fabricated data, not a verifiable on-chain event. Anyone who verifies the txHash on-chain will find nothing.

Specifications

Features:

• Tips are settled as real on-chain transactions using ethers.js
• The txHash recorded in the notarization record is verifiable on the target network

Tasks:

• Use src/services/serviceAccount.ts sendTransaction() to create a real on-chain transfer
• Replace mock fields with real values: senderAddress = await getServiceAddress(), chainId = network.chainId
• Store the real txHash from the transaction receipt
• Add error handling for failed on-chain transactions (return 502 with retry advice)

Impacted Files:

• src/app/api/tipping/route.ts
• src/services/serviceAccount.ts
• .env.example

Acceptance Criteria

• Tip transaction hashes are verifiable on the configured blockchain network
• Failed on-chain transactions return HTTP 502, not a success with a fake hash
• senderAddress and chainId reflect real network values