MVVM diagrams

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Make diagrams showing full chain of data access to display for:

• Events page showing tables of Events, either All of Pending.
• Single Event page showing full details of a single (selected) Event.
• Units page showing callsign, crew, meal break and shift times, status, notes and destination for all connected Units.
• Create an architecture diagram: see sub-issue.

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Added checklist item for overall architecture diagram. This is being created as dispatch_architecture.drawio.

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Converted architecture diagram checklist item to a sub-issue.