backend: add strong typing and tests for /health endpoint

[nazneen-p1]

Summary

This PR adds explicit TypeScript typing for the /health endpoint and includes a Vitest test to ensure it consistently returns the expected response.

Closes #2

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Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• UI / Design change
• Tests only
• Documentation
• Infrastructure / DevOps
• Security

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What Changed

• Added a TypeScript type (HealthResponse) for the /health endpoint in apps/backend/src/app.ts
• Updated the /health route to return { status: 'ok' }
• Added a test file (apps/backend/src/tests/app.test.ts) to verify the endpoint returns status 200 and correct response
• Skipped Prisma and Redis plugins during test environment to avoid database dependency issues

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How to Test

1. Run pnpm install
2. Run pnpm --filter @devcard/backend test
3. Verify that all tests pass, including the /health endpoint test

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Checklist

• My code follows the project's coding style (pnpm -r run lint passes).
• TypeScript compiles without errors (pnpm -r run typecheck).
• I have added or updated tests for the changes I made.
• All tests pass locally (pnpm -r run test).
• I have updated documentation where necessary.
• No new console.log or debug statements left in the code.
• Breaking changes are documented in this PR description.

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Additional Context

The /health endpoint is a simple status check, so no database connection is required. Prisma and Redis plugins are conditionally skipped in the test environment to ensure tests run reliably without requiring external services.

[nazneen-p1]

Hi @ShantKhatri,

I have completed the implementation and all tests are passing locally.

The Vercel check appears to require authorization, so it might be failing due to permission.

Kindly review the PR.