fix: close embedded pickers with Escape

[AlexAndBear]

Description

The file picker, location picker and "Save as" dialog of apps embed the files app in an iframe and move the focus into it. Key events of an iframe stay in its document, so the Escape handling of the surrounding modal never gets them – Escape did nothing.

In embed mode, Escape now cancels like the cancel button (posts opencloud-embed:cancel), bound via useKeyboardActions, so it works for all three pickers and any other embedding – like Escape in native file dialogs. As with all keyboard actions, it doesn't apply while a text field has the focus or a modal is open inside the embedded app.

Related Issue

• Fixes Escape doesn't close the file picker and other embedded pickers #3629

How Has This Been Tested?

• test environment: unit tests (Vitest), EmbedActions.spec.ts
• test case 1: Escape cancels in file picker, location picker and plain embed mode
• test case 2: Escape doesn't cancel while a modal is open inside the embedded app
• test case 3: other keys don't cancel

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)