feat: implement Linphone SDK integration with video call support

Complete rewrite from stub plugin to (probably) functional liblinphone integration featuring:
- Core SDK bridge with registration, calls, and media controls
- Platform views for remote and local video rendering
- Event channels for registration and call state updates

ios/Classes/Views/RemoteView.swift

@@ -0,0 +1,27 @@
+import Flutter
+import linphonesw
+
+class RemoteView: NSObject, FlutterPlatformView {
+    private var _lvvh: LinphoneVideoViewHolder? = nil
+    private var _view: UIView? = nil
+
+    init(
+        frame: CGRect,
+        viewIdentifier viewId: Int64,
+        arguments args: Any?,
+        binaryMessenger messenger: FlutterBinaryMessenger?,
+        cacher: (UIView) -> Void
+    ) {
+        super.init()
+        
+        _lvvh = LinphoneVideoViewHolder { view in
+            self._view = view
+        }
+        
+        cacher(_view!)
+    }
+
+    func view() -> UIView {
+        return _view!
+    }
+}