Captures the design decisions from the brainstorming session:
- OpcUaEndpointConfig POCO + validator + serializer in Commons
- Single source of truth: both UI and site runtime consume the model
- Typed nested JSON storage (camelCase), legacy flat-dict fallback
- Shared <OpcUaEndpointEditor> Blazor component used twice
- Custom protocol removed from dropdown; Protocol field hidden
- Validation timing on Save only; per-field red text via ValidationEntry
