nd-to-end loan lifecycle test with in-memory mock infrastructure

[Adeyemi-cmd]

close #28

PR Description

Summary

Adds a full end-to-end loan lifecycle test suite covering the complete
flow from wallet authentication through full loan repayment. All
external dependencies (Supabase, Soroban, Stellar contract clients,
Redis cache) are mocked with an in-memory store so tests run in
isolation without a live testnet.

Changes

New files

• test/e2e/loan-lifecycle.e2e-spec.ts — 13 tests across 8
  describe blocks: Auth Flow, Learner Profile, Vendor Setup, Loan
  Application, Loan Approval, Installment Repayment, Reputation Check,
  Full Repayment.
• test/e2e/helpers/test-wallet.ts — createTestKeypair() (wraps
  Keypair.random) and signMessage() (wraps Keypair.sign).
• test/e2e/helpers/test-setup.ts — buildTestApp() creates a
  NestJS test module with all required modules imported and provider
  overrides for Supabase, Soroban, all 5 contract clients, and
  CACHE_MANAGER. Includes InMemoryStore (per-table row storage)
  and MockQueryBuilder (handles select/insert/upsert/update/delete
  with eq/is/in filters, sort, range, limit).

Modified files

• test/__mocks__/stellar-sdk.js — Extended the auto-applied mock
  with Keypair.fromPublicKey (returns { verify: fn(() => true) }),
  Keypair.random (returns { sign, verify, publicKey }), Account
  class, and Horizon.Server mock.
• src/modules/reputation/reputation.controller.ts — Swapped route
  registration order so @Get('me') is declared before
  @Get(':wallet') to prevent Express from matching me as a wallet
  parameter.