feat: add wallet transaction history page

[hillbertwang]

Summary

Closes #6.

Adds a new /history page for wallet transaction history. The page uses the connected Freighter wallet address and reads recent Stellar testnet operations from Horizon instead of displaying static mock data.

• Fetches recent account operations from NEXT_PUBLIC_HORIZON_URL, defaulting to Stellar testnet Horizon
• Classifies outgoing wallet operations as contributions, incoming payments as payouts, and other wallet activity as group joins
• Displays transaction type, timestamp, amount/asset, and transaction hash
• Links each transaction hash to Stellar Expert
• Handles wallet connect, Freighter install, loading, empty, error, and refresh states
• Adds a History link to the navbar

Test plan

• git diff --cached --check passed before commit
• C:\Users\14769\make-money\sorosave-sdk\node_modules\.bin\tsc.cmd passed after checking out sorosave-protocol/sdk as the missing workspace package
• C:\Users\14769\make-money\sorosave-frontend\node_modules\.bin\next.cmd build passed with the SDK workspace linked locally
• Build emitted existing Stellar SDK dependency-chain webpack warnings around sodium-native / require-addon, but completed successfully and generated /history

/claim #6