Complete OPC UA data flow: binding UI, flattening connections, real OPC UA client

- Add connection binding UI to Instances page (per-attribute and bulk assign)
- FlatteningService populates Connections dict from bound data connections
- Real OPC UA client using OPC Foundation SDK for live tag subscriptions
- DataConnectionFactory uses RealOpcUaClientFactory by default
- OpcUaDataConnection supports both "endpoint" and "EndpointUrl" config keys

src/ScadaLink.TemplateEngine/Flattening/FlatteningService.cs

@@ -77,6 +77,25 @@ public class FlatteningService
             // Step 7: Resolve alarm on-trigger script references to canonical names
             ResolveAlarmScriptReferences(alarms, scripts);
 
+            // Step 8: Collect connection configurations for deployment packaging
+            var connections = new Dictionary<string, ConnectionConfig>();
+            foreach (var attr in attributes.Values)
+            {
+                if (attr.BoundDataConnectionId.HasValue &&
+                    !string.IsNullOrEmpty(attr.BoundDataConnectionName) &&
+                    !connections.ContainsKey(attr.BoundDataConnectionName))
+                {
+                    if (dataConnections.TryGetValue(attr.BoundDataConnectionId.Value, out var conn))
+                    {
+                        connections[attr.BoundDataConnectionName] = new ConnectionConfig
+                        {
+                            Protocol = conn.Protocol,
+                            ConfigurationJson = conn.Configuration
+                        };
+                    }
+                }
+            }
+
             var config = new FlattenedConfiguration
             {
                 InstanceUniqueName = instance.UniqueName,
@@ -86,6 +105,7 @@ public class FlatteningService
                 Attributes = attributes.Values.OrderBy(a => a.CanonicalName, StringComparer.Ordinal).ToList(),
                 Alarms = alarms.Values.OrderBy(a => a.CanonicalName, StringComparer.Ordinal).ToList(),
                 Scripts = scripts.Values.OrderBy(s => s.CanonicalName, StringComparer.Ordinal).ToList(),
+                Connections = connections.Count > 0 ? connections : null,
                 GeneratedAtUtc = DateTimeOffset.UtcNow
             };