test: add HTTP-layer route tests for Fastify API using fastify.inject

[collinsezedike]

Summary

• Adds apps/api/src/__tests__/routes.test.ts with 20 tests covering all Fastify route groups via fastify.inject, so no live RPC endpoint is needed
• Mocks @meridian/stellar-sdk-helpers at the module level; all tests run in isolation with controlled SDK responses
• Coverage: GET /health, GET /positions/:publicKey (200/400/503), POST /tx/deposit (200/400/500), POST /tx/withdraw (200/400/500), POST /tx/add-trustline (200/400), POST /tx/submit (200/400), GET /vaults (200/500), GET /vaults/:vaultId (200/404)

Test plan

• pnpm lint && pnpm typecheck && pnpm test pass locally
• pnpm --filter @meridian/api run test shows 20 passing
• No live RPC calls made during test run (confirmed by mocking @meridian/stellar-sdk-helpers)

Closes #238

[vercel]

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Project	Deployment	Actions	Updated (UTC)
meridian	Ready	Preview, Comment	Jun 24, 2026 3:30pm