🐛 Fix Shopify Custom Pixel actions being marked as background events, flatten ui_extension_errored context

[lierniel]

Motivation

RUM-18056

Two related fixes to the Shopify Custom Pixel integration:

1. Clicks tracked via startAction/stopAction in the Custom Pixel sandbox were always being reported with view.in_foreground: false. The pixel runs in a sandboxed iframe with no focusable UI, so document.hasFocus() always returns false there, which pageStateHistory.ts interprets as the page being backgrounded — even when the customer is actively on the checkout page.
2. Addresses review feedback on #4878: the ui_extension_errored error context nested an extension: { name, target, type, appName } object whose type field read as the same concept as the SDK's own error-name-derived type, but is actually an unrelated Shopify UiExtensionErrorType enum (e.g. EXTENSION_USAGE_ERROR).

Changes

• patchSandboxedIframeApis.ts: shims document.hasFocus() to always return true inside the Custom Pixel sandbox, alongside the existing cookieStore/navigator.locks/contentWindow shims for that same sandboxed context.
• shopifyBindings.ts: flattens the ui_extension_errored context and renames type to extensionErrorType to disambiguate it from the SDK's own error type. Also forwards appId and appVersion, which Shopify includes on the error payload but weren't previously captured.
• Updated shopifyBindings.spec.ts for the new flattened shape.

Test instructions

• yarn test:unit --spec packages/browser-rum-shopify/src/domain/shopifyBindings.spec.ts passes

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	180.44 KiB	180.44 KiB	0 B	0.00%	✅
Rum Profiler	8.43 KiB	8.43 KiB	0 B	0.00%	✅
Rum Recorder	21.12 KiB	21.12 KiB	0 B	0.00%	✅
Logs	57.04 KiB	57.04 KiB	0 B	0.00%	✅
Rum Salesforce	N/A	138.47 KiB	N/A	N/A	N/A
Rum Slim	138.47 KiB	138.47 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	200.16 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.43 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	3.72 KiB	N/A	N/A	N/A

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 0.00%
• Overall Coverage: 77.19% (-0.02%)

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[BenoitZugmeyer]

nitpick: usually we use snake_case for attributes