feat: implement activity history page with timeline and CSV export

[Francis6-git]

This PR implements a centralized Activity History page as requested in issue #340. It provides users with a comprehensive view of all stream-related events where they are either the sender or the recipient.

Key Changes

• New Route (/app/activity): Created a dedicated page for tracking global stream events.
• Event Timeline UI: Implemented a responsive, alternating timeline layout using Tailwind CSS to visualize the lifecycle of streams.
• Smart Filtering: Added tab-based filtering for specific event types (CREATED, WITHDRAWN, TOPPED_UP, CANCELLED, PAUSED/RESUMED).
• Infinite Scrolling: Implemented "Load More" pagination logic with state management to handle large datasets efficiently.
• Data Portability: Added a CSV export utility that allows users to download their activity history for external bookkeeping.
• Stellar Integration: Connected event hashes to the Stellar Expert explorer (Testnet) for transparent transaction verification.

Closes #340