fix: load login background video from local asset instead of network URL

VideoPlayerController.networkUrl(Uri.parse('assets/login-bg.mp4')) silently
fails because 'assets/login-bg.mp4' is not a valid HTTP URL — the video
never initializes and the login screen shows a plain black background.

Fix: switch to VideoPlayerController.asset() and register the file in
pubspec.yaml. The MP4 is gitignored (22 MB) and kept local for builds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pubspec.yaml

@@ -34,6 +34,7 @@ flutter:
   assets:
     - assets/images/
     - assets/icon/hand_stop.svg
+    - assets/login-bg.mp4
   fonts:
     - family: Gilroy
       fonts: