[NpWebApi2] Add sceNpWebApi2PushEventCreateFilter stub (#503)

Add sceNpWebApi2PushEventCreateFilter (NID: MsaFhR+lPE4) to the
libSceNpWebApi2 module. This function is called by Unity games
during initialization and was unresolved, causing an import warning
and returning ORBIS_GEN2_ERROR_NOT_FOUND.

The stub validates the library context and returns an incrementing
filter handle, following the same pattern as the existing
sceNpWebApi2PushEventCreateHandle.

NID sourced via:
  python scripts/aerolib_catalog.py lookup MsaFhR+lPE4

Co-authored-by: tru3 <tru3@tru3.com>

src/SharpEmu.Libs/Np/NpWebApi2Exports.cs

@@ -37,6 +37,24 @@ public static class NpWebApi2Exports
         return ctx.SetReturn(libraryContextId);
     }
 
+    [SysAbiExport(
+        Nid = "MsaFhR+lPE4",
+        ExportName = "sceNpWebApi2PushEventCreateFilter",
+        Target = Generation.Gen4 | Generation.Gen5,
+        LibraryName = "libSceNpWebApi2")]
+    public static int NpWebApi2PushEventCreateFilter(CpuContext ctx)
+    {
+        var libraryContextId = unchecked((int)ctx[CpuRegister.Rdi]);
+        if (!IsValidLibraryContextId(libraryContextId))
+        {
+            return ctx.SetReturn(NpWebApi2ErrorInvalidArgument);
+        }
+
+        var filterHandle = Interlocked.Increment(ref _nextPushEventHandle);
+        TraceNpWebApi2("push-event-create-filter", libraryContextId, (ulong)filterHandle);
+        return ctx.SetReturn(filterHandle);
+    }
+
     [SysAbiExport(
         Nid = "WV1GwM32NgY",
         ExportName = "sceNpWebApi2PushEventCreateHandle",