fix(commons): LoadLegacy handles mixed-type JSON values (number/bool/string)

src/ScadaLink.Commons/Serialization/OpcUaEndpointConfigSerializer.cs

@@ -118,8 +118,27 @@ public static class OpcUaEndpointConfigSerializer
 
     private static OpcUaEndpointConfig LoadLegacy(string json)
     {
-        var dict = JsonSerializer.Deserialize<Dictionary<string, string>>(json)
-                   ?? new Dictionary<string, string>();
+        using var doc = JsonDocument.Parse(json);
+        if (doc.RootElement.ValueKind != JsonValueKind.Object)
+            throw new JsonException("Legacy JSON must be a flat object.");
+
+        var dict = new Dictionary<string, string>();
+        foreach (var prop in doc.RootElement.EnumerateObject())
+        {
+            // JsonElement.ToString() returns the raw value for primitives:
+            // "1000" for numbers, "true"/"false" for booleans, the string content
+            // for strings. Nested objects/arrays serialize to their JSON; we don't
+            // expect those in the legacy flat-dict shape, but FromFlatDict will
+            // simply ignore unknown keys.
+            dict[prop.Name] = prop.Value.ValueKind switch
+            {
+                JsonValueKind.String => prop.Value.GetString() ?? "",
+                JsonValueKind.Number => prop.Value.GetRawText(),
+                JsonValueKind.True => "True",
+                JsonValueKind.False => "False",
+                _ => prop.Value.ToString()
+            };
+        }
         return FromFlatDict(dict);
     }