[EPIC E7] Build standalone ZorgDossier source application

[JorisHeadease]

Build ZorgDossier as a standalone source EHR that proves data crosses the GF chain from a visibly independent application.

Work items

• Split the source guise from demo-ehr into a separate application and port.
• Give ZorgDossier its own brand, layout and green visual system.
• Open it in a separate browser tab from the sandbox marker path.
• Add an allergy entry form with a free-text marker using the DEMO- prefix convention.
• Add an explicit NVI registration checkbox and reuse the idempotent /nvi/List path.
• Tag user-created resources so reset can remove them from FHIR and the NVI.

Acceptance criteria

• ZorgDossier is visually and operationally independent from Plataan EHR.
• A user-created record is found and retrieved exclusively through the GF chain.
• The marker appears highlighted in the enriched Plataan record.
• Reset removes the user-created resource and its NVI registration.

Frontend constraint

Use vendored Datastar as the initial frontend implementation. Keep backend routes, the step-event JSON schema, CSS/design tokens and the framework-free journey-map driver independent of Datastar. If the documented fallback triggers occur, the AI-assisted migration replaces Datastar with buildless Preact + htm in one cutover.

Integration validation depends on #544 and #542.

Refs #532
Refs #538