feat: Initial Test Suite for Chat App

[kwsantiago]

Summary

Basic test infrastructure done but missing core requirements from #61

Completed

• CI/CD pipeline with GitHub Actions
• Vitest setup with 53 passing tests
• Basic Cashu mint API testing with FakeWallet
• Component unit tests
• Error handling coverage

Still Needed

• Real Lightning node integration (currently using FakeWallet)
• Mock Nostr relay for chat testing
• Multi-user payment flows
• Message routing and failure scenarios
• State persistence tests
• Restore deleted invoice tests and regtest scripts

[vercel]

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