Added tests which guard the prompts and the protected data of visual briefings

app/Tests/Serialization/Fixtures/visual-briefing-protected-data.json

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+{"slots":{"title":"Gr\u00F6\u00DFe"},"_mwai":{"schemaVersion":2,"runtimeVersion":1,"aiStudioVersion":"__VERSION__","assets":{"asset-1":"data:image/png;base64,AA=="},"assetMetadata":{"asset-1":{"description":"A chart of the quarter","altText":"Revenue per quarter, with Gr\u00F6\u00DFe"}},"footer":{"createdWith":"Created with MindWork AI Studio v__VERSION__.","models":"Contributing models: Model A (content); Model B (presentation).","createdAt":"Revision created on 2026-11-03.","authors":"Author(s): author sample 4.","protection":"Protection level: internal."}}}