FAQ seed: quick start, deployment, login, migration, and smoke tests

[lwnmengjing]

This is the initial FAQ seed. We will turn repeated questions into docs and good first issues.

Current FAQ candidates:

1. How do I run the backend locally?
2. How do I run the admin frontend locally against the alpha API?
3. Which Go, Node, and pnpm versions are expected?
4. How should TimescaleDB/PostgreSQL and Redis be configured?
5. What should I check when login fails?
6. How do migrations work?
7. How do I verify Swagger/API changes?
8. What is the alpha/beta/prod environment policy?
9. How do I prepare a useful bug report?
10. Which tasks are good first contributions?

Reply with the FAQ item that blocks you most. If the question is common enough, we will move it into docs and link the final answer here.