Add a developer troubleshooting guide for local environment failures

[robertocarlous]

Why
New contributors will run into common issues such as missing env vars, database connectivity, Prisma schema mismatches, and health-check failures. A focused troubleshooting guide would reduce onboarding friction.

Acceptance criteria

• Cover the most common local setup failures.
• Include symptoms, root causes, and fix steps.
• Link the guide from the README and setup documentation.

[BigJohn-dev]

I’m interested in solving meaningful engineering problems and improving real-world software. I have experience with backend development, OOP, APIs, Git workflows, and building maintainable full-stack applications.

[Tobi-8]

Hey maintainer, i have looked through your description, and i have had experience in this type of issue.
kindly assign