Support single-subscription events modules when reading remote configuration

[rezaansyed]

WHY are these changes introduced?

Shopify Core is adding a single-subscription shape for events app modules: the :events module config will accept either the existing subscription list (subscription: [...], one module with uid "events") or a new single-subscription object (subscription: {...}, one module per subscription, uid = subscription handle). This enables shop-scoped (imperative) event subscriptions and a migration from one list module to N single-subscription modules.

The CLI's events transforms are currently hard-typed to the list shape: transformToEventsConfig calls .map on subscription and crashes on an object, and config link would need N single-subscription modules to merge back into one [[events.subscription]] list in the local TOML.

WHAT is this pull request doing?

• transformToEventsConfig (remote → local): accepts a single-subscription object or the legacy array. Single objects are normalized to a one-element array (after stripping the server-managed identifier), so merging N single-subscription modules via deepMergeObjects implodes them into one subscription list in the TOML.
• transformFromEventsConfig (local → remote): resolves relative subscription URIs for both shapes, preserving the input shape.

The local TOML format is unchanged: [[events.subscription]] stays a list. This is read-side tolerance only.

How to test your changes?

• pnpm vitest run src/cli/models/extensions/specifications/transform/app_config_events.test.ts (14 tests, 5 new covering single-object stripping, multi-module merge, mixed-shape merge, and relative-URI resolution for the object shape).

Post-release steps

None.

Measuring impact

• n/a: covered by existing events module metrics in Core

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes