feat: Add deprecation notice for global Dbpool and Ctx variables

- Enhanced TODO comment to clearly mark Dbpool and Ctx as DEPRECATED
- Direct developers to use Database struct from database.go instead
- Migration test already includes manual data insertion (5 games, 8 songs)

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/db/dbHelper.go

@@ -20,7 +20,9 @@ import (
 	"go.uber.org/zap"
 )
 
-// TODO: Remove these global variables once test_helpers.go is fully migrated to use Database struct
+// TODO: DEPRECATED - Remove these global variables once all code is migrated to use Database struct
+// Use database.go's Database struct instead. These globals remain for backward compatibility
+// with legacy code paths. New code should use the Database struct from database.go.
 var Dbpool *pgxpool.Pool
 var Ctx = context.Background()