svc-vision: camera live view, moved from app-flutter's test tool

Camera-agnostic (--camera auto finds any V4L2 capture device and finds it
again after a replug; non-MJPEG cameras are encoded), says when the camera
is unavailable, paced per decision 28. Python, standard library only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

.gitignore

@@ -0,0 +1,2 @@
+__pycache__/
+*.pyc