fix(mollie-payments): wrap addPayment in transaction

[casperiv0]

This PR includes:

With the recent release of Vendure, it requires the transitionOrderToState and addPaymentToOrder fns to be wrapped in a Transaction.
That wasn't handled inside the addPayment helper function in the Mollie service.

cc @martijnvdbrug would be nice to have your input on this too, please 🙏

Related Vendure Core PR: vendurehq/vendure#4689

---

^{Need help on this PR? Tag @codesmith with what you need.}

• Let Codesmith autofix CI failures and bot reviews

[martijnvdbrug]

Minor optional change requested, but approved if you choose to ignore it :-)

Good catch. I have yet to test it out though...

[casperiv0]

Thanks Martijn! Tested in my Vendure project w/ our test suite and are passing now after this change. Before they were failing, mentioning that the fn wasn't wrapped in a transaction

[grolmus]

Reviewed locally + ran build & lint, both green.

The wrap pattern is correct and matches the canonical Vendure idiom mirroring core #4689. withTransaction correctly joins an existing tx on _ctx (webhook path via @Transaction() on MollieController) and opens a new one when _ctx has none (free-order path in createPaymentIntent where a fresh admin RequestContext is built). Applying the wrap at addPayment rather than higher up in handleMolliePaymentStatus is the right call — it also protects the free-order path and any future direct callers.

A few non-blocking suggestions for a follow-up:

1. Param naming: _ctx is a touch confusing — the leading underscore conventionally signals an unused parameter, but here it's passed to withTransaction. Something like outerCtx would read better. Minor.

2. Comment clarity at the top of addPayment: the current note mentions the free-order admin ctx specifically, but addPayment is a public method and any future caller without an outer tx would hit the same issue. Could be reworded to lead with the general invariant — "transitionToState and addPaymentToOrder must run in a single tx so save/hooks/save commit or roll back together; withTransaction joins an existing tx on the passed ctx, or opens a new one (e.g. for the fresh admin ctx in createPaymentIntent free-order branch)."

3. E2E regression: core #4689 added order-process-rollback.e2e-spec.ts as a regression guard. A sibling spec in packages/mollie-plugin/e2e/ that registers a throwing hook and asserts no half-transitioned state after addPayment failure would protect against future refactors. Worth tracking as a follow-up issue.

LGTM, approving.