chore: upgrade melos to 7.5.1 with pub workspaces and dep catalog

- Upgrade Melos to 7.5.1 using Dart pub workspaces (Melos 7 paradigm).
- Replace per-package pubspec_overrides.yaml with workspace-native resolution. Add dependencies.yaml as a centralized catalog for all external deps with sync_deps.dart tool to propagate and validate versions across the monorepo.

packages/sca_treezor/pubspec.yaml

@@ -3,6 +3,7 @@ description: "A new Flutter package project."
 version: 0.0.1
 homepage:
 publish_to: 'none' # Remove this line if you wish to publish to pub.dev
+resolution: workspace
 
 environment:
   sdk: ^3.9.2

packages/sca_treezor/pubspec_overrides.yaml

@@ -1,4 +0,0 @@
-# melos_managed_dependency_overrides: flutter_treezor_entrust_sdk_bridge
-dependency_overrides:
-  flutter_treezor_entrust_sdk_bridge:
-    path: ../flutter_treezor_entrust_sdk_bridge