Add a seed script for local development

[Glittersup]

Summary

A newly reset database serves empty responses, which makes the API awkward to explore or demonstrate locally. A seed script that inserts a few representative streams removes that friction.

Acceptance criteria

• A seed script inserts a small set of representative streams.
• The seeded data covers a pending, an active and a cancelled stream.
• The README documents how to run it.

Getting started

Fork this repository, clone your fork, and add this repo as upstream:

git clone https://github.com/<your-username>/tricklepay-backend.git
cd tricklepay-backend
git remote add upstream https://github.com/TricklePay/tricklepay-backend.git

Create a branch for this issue:

git checkout -b chore/issue-168

Suggested commit message:

chore: add a local seed script

Run npm run typecheck, npm test, and npm run build before opening a pull request and linking this issue.