Restore global.json file to proper state

- Restored global.json content that was accidentally emptied in commit 05a6385
- Proper .NET 9.0.100 SDK configuration restored
- File now contains correct SDK version and rollForward settings

Co-authored-by: reakaleek <[email protected]>

Author: Copilot

global.json

@@ -0,0 +1,7 @@
+{
+  "sdk": {
+    "version": "9.0.100",
+    "rollForward": "latestFeature",
+    "allowPrerelease": false
+  }
+}