feat(videocall): add videocall_sdk package wrapping Juphoon jc_sdk

Full wrapper around jc_sdk v2.16.5 with clean architecture:
- 7 services covering 100% of jc_sdk public API (Client, Call, Device, Channel, Push, Net, Log)
- Constructor injection with GetIt DI module (follows sca_treezor pattern)
- VideocallSdkManager orchestrator for init/destroy lifecycle
- VideocallSdkConfig abstract for environment-specific AppKey
- Stream-based callbacks for reactive UI consumption
- Riverpod providers (service + stream) for feature layer
- AppKey configured per environment via dart-define-from-file
- Integrated in init_app.dart alongside scaTreezorModule

pubspec.yaml

@@ -36,6 +36,7 @@ workspace:
   - packages/sf_shared
   - packages/sf_tracking
   - packages/utils
+  - packages/videocall_sdk
 
 dependencies:
   flutter_secure_storage: ^9.2.4