Avoid duplicate app lookups for Function schemas

[dmerand]

WHY are these changes introduced?

Function schema generation already has the app ID from linked app context. The client looks up the app again only to recover that same ID.

WHAT is this pull request doing?

Pass the resolved app ID through schema generation and request the schema directly from Functions. This removes one duplicate App Management lookup per fetched schema, for either target-based or API-type queries. It does not remove initial context or access checks.

Keep the numeric Functions URL, schema contents and version header, stdout/file behavior, and existing-schema fast path unchanged.

Use the PR snapshot from a linked Function directory for the manual commands below. Check both target-based and API-type configurations.

How to manually test your changes?

shopify app function schema --stdout
shopify app function schema

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add