Unify API route parameters, return IResult everywhere, merge picture upload DTOs and centralize validation limits

Guid and long route constraints, id/trackId parameter names, Update*Request without the New prefix,
sentence-case operation summaries, shared security scheme id and a single Limits class.

backend/Hosts/Musify.Api/DataTransferObjects/Albums/RequestAlbumPictureUploadRequest.cs

@@ -1,6 +0,0 @@
-namespace Musify.Api.DataTransferObjects.Albums;
-
-public record RequestAlbumPictureUploadRequest(
-    string FileType,
-    string ContentType,
-    long? ExpectedSizeBytes = null);

backend/Hosts/Musify.Api/DataTransferObjects/Albums/UpdateAlbumRequest.cs

@@ -1,7 +1,7 @@
 namespace Musify.Api.DataTransferObjects.Albums;
 
 public record UpdateAlbumRequest(
-    string NewTitle,
-    string? NewDescription,
-    int? NewReleaseYear,
-    Guid? NewPictureIntentId);
+    string Title,
+    string? Description,
+    int? ReleaseYear,
+    Guid? PictureIntentId);

backend/Hosts/Musify.Api/DataTransferObjects/PictureUploadRequest.cs

@@ -0,0 +1,6 @@
+namespace Musify.Api.DataTransferObjects;
+
+public record PictureUploadRequest(
+    string FileType,
+    string ContentType,
+    long? ExpectedSizeBytes = null);

backend/Hosts/Musify.Api/DataTransferObjects/PlayLists/RequestPlayListPictureUploadRequest.cs

@@ -1,6 +0,0 @@
-namespace Musify.Api.DataTransferObjects.PlayLists;
-
-public record RequestPlayListPictureUploadRequest(
-    string FileType,
-    string ContentType,
-    long? ExpectedSizeBytes = null);

backend/Hosts/Musify.Api/DataTransferObjects/PlayLists/UpdatePlayListRequest.cs

@@ -3,7 +3,7 @@ using Musify.Domain.ValueObjects;
 namespace Musify.Api.DataTransferObjects.PlayLists;
 
 public record UpdatePlayListRequest(
-    string? NewName,
-    string? NewDescription,
-    Guid? NewPictureIntentId,
-    PlayListVisibility? NewVisibility = null);
+    string? Name,
+    string? Description,
+    Guid? PictureIntentId,
+    PlayListVisibility? Visibility = null);