core: implement transaction history with Stellar Expert links

[EmeditWeb]

Problem

Users have no way to see their on-chain transaction
history in the web app.

What To Build

Build /history page with:

1. Transaction timeline (most recent first)
2. Filter controls (by type, date range, status)
3. CSV export
4. Expandable transaction details
5. Pending transactions section

Files To Touch

• src/pages/History.tsx (new)
• src/services/history.service.ts (new)
• src/router/index.tsx

Acceptance Criteria

• All transaction types shown
• Stellar Expert links correct
• Filter and date range work
• CSV export works
• npm run build passes

Mandatory Checks Before PR

• npm run build passes
• No any types
• PR references this issue

[Godfrey-Delight]

I'd like to work on this. I'll build a transaction history view that fetches the user's on-chain transactions via the Stellar SDK and displays them in a paginated list. PR within 48 hours.