Add multi-stream view... list all streams for a connected wallet

[Ali6nXI]

Overview

Currently the dashboard shows a static list of streams. We need a proper
multi-stream view that fetches and displays all active streams associated
with the connected wallet address — both as sender and recipient.

Tasks

• Add a getStreamsByWallet(walletAddress) helper in
  frontend/src/services/stellar.ts
• Query contract events (StreamCreated) to build the stream index
  for a given wallet
• Update Dashboard.tsx to auto-fetch streams on wallet connect
• Display two tabs: "Sending" and "Receiving" streams
• Show loading skeleton while streams are fetching
• Handle empty state gracefully ("No active streams yet")
• Mobile-friendly layout (most Nigeria users are on mobile)
• Open a PR with screenshots of the updated dashboard

Acceptance Criteria

• Connecting a wallet automatically loads all streams
• Streams are correctly split into Sending / Receiving tabs
• Works on Stellar testnet with real contract data
• UI is responsive on mobile screens

Resources

• Stellar SDK event querying: https://developers.stellar.org/docs
• Freighter API: https://docs.freighter.app
• Contract: contracts/stellar-drips/src/lib.rs