Add upgrade testing script and update progress notes

UPGRADE_NOTES.md

@@ -121,6 +121,9 @@
 - Fabric.js designer tool is front-end only, won't be affected
 
 ## Completed Steps
-1. ✅ Created feature branch
-2. ✅ Documented current state
-3. ⏳ Ready to start first upgrade
+1. ✅ Created feature branch (`feature/laravel-upgrade`)
+2. ✅ Documented current state and dependencies
+3. ✅ Created baseline tag (`v5.0-baseline`) for rollback
+4. ✅ Updated composer.json for Laravel 5.1
+5. ✅ Updated Guzzle 5.0 → 6.0 (required for Laravel 5.1)
+6. ⏳ Next: Build container and run composer update