Add a database reset script

[Glittersup]

Summary

Resetting the local database is a routine step when working on the indexer, and it currently takes several manual commands. A single script makes it repeatable and safe to document.

Acceptance criteria

• A script resets the local database to an empty schema.
• It refuses to run against a non-local database.
• The README documents 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-167

Suggested commit message:

chore: add a database reset script

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