Add App Events logging API

[kristianpd]

Description

Adds the Ruby SDK counterpart to shopify-app-js App Events logging:

• ShopifyAPI.log validates and posts one App Event to the Global API.
• ShopifyAPI::Auth::GlobalApiClientCredentials.global_api_client_credentials mints and caches the app-level JWT.
• ShopifyAPI::Context.global_api_url supports HTTPS-only non-production Global API hosts.
• A 401 response refreshes the token once. Other HTTP errors propagate to the caller.

The request contract uses snake_case JSON, string shop IDs, the 2026-07 API version floor, and both actual and documented idempotent replay headers.

JavaScript reference: Shopify/shopify-app-js#3368

How has this been tested?

• bundle exec ruby -Ilib -Itest test/app_events_test.rb
• bundle exec ruby -Ilib -Itest test/app_events/event_payload_test.rb
• bundle exec ruby -Ilib -Itest test/auth/global_api_client_credentials_test.rb
• bundle exec rake test:library — 390 runs, 769 assertions
• bundle exec rubocop — 119 files, no offenses

bundle exec srb tc cannot run on this Apple Silicon host because the locked sorbet-static binary is x86_64-only: Bad CPU type in executable. CI must provide the typecheck result.

The live local-Core smoke minted a Global API token, then the events endpoint returned 503 Service unavailable. Core logged PG::InternalError: view 'apps.app_installations' not found in view catalog from VerifyAppInstallation; the SDK request reached the endpoint, but the local Query Engine prerequisite blocked event ingestion.

Checklist:

• My commit message follows the documented pattern.
• I have performed a self-review of my own code.
• I have added tests that prove my feature works.
• I have updated the project documentation.
• I have added a changelog line.