Pin .NET SDK 10.0.403

All repository SDK selection and GitHub workflows consume global.json; no other 10.0.401 pins remain. Verified JSON, effective SDK resolution, restore, format verification, and a complete strict Debug build on 10.0.403 with zero warnings and errors.

Author: KSemenenko

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "10.0.401",
+    "version": "10.0.403",
     "rollForward": "patch",
     "allowPrerelease": false
   },