refactor: Revert Nth frame processing in webcam mode

Reverts the Nth frame processing logic previously introduced in
modules/ui.py (create_webcam_preview function). Webcam frames
will now be processed by the full pipeline on every frame,
instead of skipping frames.

This change is based on your feedback requesting to focus on
optimizing the per-frame performance rather than using frame
skipping techniques at this stage.

modules/ui.py

@@ -988,9 +988,6 @@ def create_webcam_preview(camera_index: int):
 
     # --- End Source Image Loading ---
 
-    detection_frame_counter = 0
-    DETECTION_INTERVAL = 3 # Process every 3rd frame
-
     prev_time = time.time()
     fps_update_interval = 0.5
     frame_count = 0