useTransactionHistory: add polling for new events

[Ejirowebfi]

Description

useTransactionHistory.ts fetches events once on mount. New transactions are not reflected until the user manually refreshes. Polling every 30 seconds would keep the history current.

Tasks

• Add a setInterval (30 s) in useTransactionHistory to re-fetch events
• Clear the interval on component unmount
• Show a "Last updated X seconds ago" indicator
• Add a manual "Refresh" button as an alternative

Acceptance Criteria

• New events appear within 30 seconds without a page refresh
• Interval is cleared when the component unmounts (no memory leak)
• Manual refresh button triggers an immediate fetch