Refactor AnnotationCreateDto and update appsettings.json

Refactored the `AnnotationCreateDto` class:
- Changed `ElementId` from `int` to `long` and made it mutable.
- Marked `Name`, `Value`, and `Type` as `[Obsolete]` with defaults.
- Added `[Obsolete]` attributes to `Width` and `Height`.
- Introduced a new `Page` property to replace `SignatureDto`.

Updated `appsettings.json`:
- Set `Api.BaseUrl` to an empty string.

EnvelopeGenerator.ReceiverUI/wwwroot/appsettings.json

@@ -1,6 +1,6 @@
 {
   "Api": {
-    "BaseUrl": "https://localhost:8088",
+    "BaseUrl": "",
     "ForceToUseFakeDocument": true
   }
 }