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

example/ios/Podfile.lock

@@ -0,0 +1,36 @@
+PODS:
+  - Flutter (1.0.0)
+  - integration_test (0.0.1):
+    - Flutter
+  - liblinphone_flutter (0.0.2):
+    - Flutter
+    - linphone-sdk (~> 5.2.0)
+  - linphone-sdk (5.2.114)
+
+DEPENDENCIES:
+  - Flutter (from `Flutter`)
+  - integration_test (from `.symlinks/plugins/integration_test/ios`)
+  - liblinphone_flutter (from `.symlinks/plugins/liblinphone_flutter/ios`)
+  - linphone-sdk (~> 5.2.0)
+
+SPEC REPOS:
+  https://gitlab.linphone.org/BC/public/podspec.git:
+    - linphone-sdk
+
+EXTERNAL SOURCES:
+  Flutter:
+    :path: Flutter
+  integration_test:
+    :path: ".symlinks/plugins/integration_test/ios"
+  liblinphone_flutter:
+    :path: ".symlinks/plugins/liblinphone_flutter/ios"
+
+SPEC CHECKSUMS:
+  Flutter: cabc95a1d2626b1b06e7179b784ebcf0c0cde467
+  integration_test: 252f60fa39af5e17c3aa9899d35d908a0721b573
+  liblinphone_flutter: 704c79aa1453d588208c101dd5b54077cf8c1a44
+  linphone-sdk: dfe70cd91cd826e1a6833f349525a305f11b438c
+
+PODFILE CHECKSUM: d42999c5f93753f05e2705e1d227f627884c6aed
+
+COCOAPODS: 1.16.2