chore: remove the CoinPayPortal invoice workflow

[sweidinger]

What and why

Split out of #156 so the pinning work there can be judged on its own — this one asks a different question, whether the workflow should exist at all, and that is your call rather than a mechanical fix. The two PRs are independent and can merge in either order.

coinpay.yml runs profullstack/coinpaybot@v0 on every issue comment starting with /coinpay, holding issues: write and pull-requests: write, against COINPAY_API_KEY and COINPAY_BUSINESS_ID. Neither secret is set on this repository, so the step cannot have succeeded since it landed — removing it does not take away something that works today.

What it does do is sit on the issue_comment trigger, which anyone with a GitHub account can fire by commenting on any issue or PR. The action behind it is referenced as @v0 — a tag its owner can repoint at any commit — so the code that runs on that trigger is neither fixed nor reviewed here. That is a standing write-scoped entry point into the repo in exchange for a feature a terminal torrent search client has no use for: there is nothing to invoice.

Deleting rather than pinning, because a pin would only freeze code that should not be reachable in the first place.

If this is wrong, it is easy to say so and I will close it. If the secrets are pending and the bot is meant to be live, the right change is the opposite one — set them and pin coinpaybot to a commit, which I am happy to send instead. I have no visibility into whether this is intentional tooling of yours.

Checklist

• npm run typecheck is clean
• npm test passes (45 files, 311 tests)
• New logic has a test (vitest; mock node built-ins for platform code) — n/a, deletion only
• If I added a key, I updated both HELP_GROUPS and footerHints in src/ui/keymap.ts — n/a
• If I added a Store field, I updated makeStore in scripts/render-previews-impl.tsx — n/a
• OS-touching code works on Windows, macOS, and Linux — n/a, CI config only
• One concern, with a Conventional Commits title