Document all data the UI expects to receive (response shapes, field names, optional vs. required fields)

```mermaid
---
title: Response models
---
classDiagram
Study -- SICGeneration
Study -- PatientEntry
Study -- Participation
PatientEntry -- PatientReference
PatientEntry -- Participation
BatchPatientEntry -- PatientEntry
BatchPatientEntry -- MasterData
BatchPatientEntry -- Encounter
BatchPatientEntry -- EntryValidation

class Study {
string id
string title
string description
number createdTimestamp
number closedTimestamp?
SICGeneration sicGeneration
string sicGenerator
string sicGeneratorState
Participation participation
}

class MasterData {
number birthDate
string sex
string zip
number patientId
}

class PatientEntry {
string comment?
Participation participation
string extension
string root
PatientReference reference
string sic?
number timestamp
string user
Study study
}

class Encounter {
number encounterId
number patientId
number startDate
number endDate
}

class BatchPatientEntry {
string sic?
string extension
MasterData masterData?
Encounter lastEncounter?
EntryValidation entryValidation?
}

class SICGeneration {
<>
AutoAndManual
ManualOnly
}

class Participation {
<>
OptIn
OptOut
}

class PatientReference {
<>
Billing
Encounter
Patient
}

class EntryValidation {
<>
Valid
EntryFound
SicFound
SicMissing
NoMasterdataFound
NoEncountersFound
PatientReferenceDuplicate
SicDuplicate
Pending
}
```

WIP: I am still working on a better way to model PatientEntry and BatchPatientEntryy