[backend/federation] Handle ASDelete activities of ASNote objects

Some implementations seem to send deletes of ASNote objects instead of ASTombstone objects.

Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs

@@ -85,6 +85,12 @@ public class ActivityHandlerService(
 					return;
 				}
 
+				if (activity.Object is ASNote note)
+				{
+					await noteSvc.DeleteNoteAsync(note, resolvedActor);
+					return;
+				}
+
 				if (activity.Object is not ASTombstone tombstone)
 					throw GracefulException
 						.UnprocessableEntity($"Delete activity object is invalid: {activity.Object?.Type}");

Iceshrimp.Backend/Core/Services/NoteService.cs

@@ -570,6 +570,28 @@ public class NoteService(
 		await DeleteNoteAsync(dbNote);
 	}
 	
+	public async Task DeleteNoteAsync(ASNote note, User actor)
+	{
+		// ReSharper disable once EntityFramework.NPlusOne.IncompleteDataQuery (it doesn't know about IncludeCommonProperties())
+		var dbNote = await db.Notes.IncludeCommonProperties().FirstOrDefaultAsync(p => p.Uri == note.Id);
+		if (dbNote == null)
+		{
+			logger.LogDebug("Note '{id}' isn't known, skipping", note.Id);
+			return;
+		}
+
+		// ReSharper disable once EntityFramework.NPlusOne.IncompleteDataUsage (same reason as above)
+		if (dbNote.User != actor)
+		{
+			logger.LogDebug("Note '{id}' isn't owned by actor requesting its deletion, skipping", note.Id);
+			return;
+		}
+
+		logger.LogDebug("Deleting note '{id}' owned by {userId}", note.Id, actor.Id);
+
+		await DeleteNoteAsync(dbNote);
+	}
+
 	public async Task UndoAnnounceAsync(ASNote note, User actor)
 	{
 		var renote = await ResolveNoteAsync(note);