Consolidate duplicated error handling in the routes

[Glittersup]

Summary

Each route builds its error responses independently, which is how error shapes drift apart between endpoints. A shared helper keeps them consistent as routes are added.

Acceptance criteria

• Error responses are produced through one shared helper.
• All routes use it.
• The response shapes are unchanged.

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 refactor/issue-160

Suggested commit message:

refactor: consolidate route error handling

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