perf: réduire la latence du flux MJPEG

- Pipeline 640x480@30fps au lieu de 1280x720@15fps
- appsink max-buffers=1 sync=false pour éliminer le buffering
- Suppression du time.sleep(0.066) dans generate_mjpeg

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

camera_server.py

@@ -35,10 +35,10 @@ def capture_loop():
     # Pipeline GStreamer pour CSI sur Pi Bookworm
     pipeline = (
         "libcamerasrc ! "
-        "video/x-raw,width=1280,height=720,framerate=15/1 ! "
+        "video/x-raw,width=640,height=480,framerate=30/1 ! "
         "videoconvert ! "
         "video/x-raw,format=BGR ! "
-        "appsink drop=1"
+        "appsink drop=1 max-buffers=1 sync=false"
     )
     cam = cv2.VideoCapture(pipeline, cv2.CAP_GSTREAMER)
 
@@ -71,7 +71,6 @@ def generate_mjpeg():
             + jpeg.tobytes()
             + b"\r\n"
         )
-        time.sleep(0.066)
 
 @app.route("/")
 def index():