Add pool transaction history with incremental loading

[codexbounty0611]

Fixes #29.

Summary

• Adds a pool transaction API that reads PoolDeposit, PoolWithdrawal, PoolPayIn, and PoolPayOut events from the Pool contract.
• Normalizes event data into clearer transaction rows with type, asset/market, amount, pool balance, wallet, and explorer tx link.
• Adds incremental loading with an IntersectionObserver-based infinite scroll trigger plus a Load More fallback.

Testing

• node --check src/api/pool.js
• Full Svelte build was not run because npm is not available in the local environment.