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.lock

@@ -1004,6 +1004,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.5"
+  jc_sdk:
+    dependency: transitive
+    description:
+      name: jc_sdk
+      sha256: "017148c51e6181870507d429b2e2b52df1b13168ebd9590b3a3fa86ab09274ba"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.16.5"
   js:
     dependency: transitive
     description: