feat(api): add Scalar API reference with independent toggle

Decouple Scalar from Swagger so each can be enabled/disabled separately
via the UseScalar config flag. When Scalar is enabled without Swagger,
the bare OpenAPI JSON endpoint is still registered so Scalar has a
spec to load from.

- Add UseScalar flag to appsettings.json (default: true)
- Resolve useScalar from config in Program.cs
- Map Scalar only when useScalar is true
- Ensure UseSwagger() is called if Scalar needs it but Swagger UI is off

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs

@@ -391,10 +391,19 @@ try
     }
 
     var useSwagger = app.Environment.IsDevelopment() || config.GetValue<bool>("UseSwagger");
+    var useScalar = app.Environment.IsDevelopment() || config.GetValue<bool>("UseScalar");
+
     if (useSwagger)
     {
         app.UseSwagger();
         app.UseSwaggerUI();
+    }
+
+    if (useScalar)
+    {
+        if (!useSwagger)
+            app.UseSwagger(); // Scalar requires the OpenAPI JSON endpoint
+
         app.MapScalarApiReference();
     }
 

EnvelopeGenerator.Server/EnvelopeGenerator.Server/appsettings.json

@@ -1,5 +1,6 @@
 {
   "UseSwagger": true,
+  "UseScalar": true,
   "UseDbMigration": false,
   "DiPMode": true,
   "Logging": {