test: add E2E test suite for complete BNPL flow

[Josue19-08]

🔖 Title

Add E2E test suite covering the complete BNPL loan lifecycle

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📄 Description

The codebase has 15 unit test files but lacks end-to-end tests that validate the full BNPL flow from wallet registration through loan creation, repayment, and reputation update. E2E tests are critical to catch integration regressions that unit tests miss, especially around Stellar transaction building and Supabase state transitions.

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✅ Tasks to complete

• Set up E2E test environment: dedicated Supabase test schema, mock Stellar Horizon, mock Soroban RPC
• Implement E2E test: Auth flow — register user → generate nonce → verify signature → receive JWT
• Implement E2E test: Loan flow — get quote → create loan (XDR) → submit signed XDR → verify loan status in DB
• Implement E2E test: Repayment flow — pay loan → verify payment recorded → verify loan status updated
• Implement E2E test: Liquidity flow — deposit → get pool overview → withdraw
• Implement E2E test: Notifications flow — trigger loan reminder job → verify notification created → mark as read
• Add GitHub Actions step to run E2E tests in CI with test environment variables
• Document how to run E2E tests locally in `docs/setup/`

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📚 Documentation/context for AI

(This link never should removed)
https://github.com/TrustUp-app/TrustUp-API/tree/main/docs

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🗒️ Additional notes

• Use NestJS `@nestjs/testing` `createTestingModule` with SuperTest (Fastify adapter)
• Mock Stellar SDK calls at the service boundary, not at the HTTP level
• E2E tests should run in isolation — each test must clean up its own DB records
• See `test/helpers/` for existing test utilities to reuse

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[Mystery-CLI]

I have read through the required implementations and understand what to do can i work on it?

[Delightech28]

@Delightech28 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'd like to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Delightech28 to this issue.

[Fran19-09]

@Fran19-09 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

My name is Francinni, I am a graphic designer from Costa Rica with experience in digital design, web development, and UI/UX design using technologies such as React, Angular, and more. I have worked on various projects creating visual identities and engaging digital experiences. I am passionate about designing functional and aesthetic interfaces, ensuring that every element effectively communicates the brand’s message.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Fran19-09 to this issue.