Ajuster pyramide RSSI : réduire à 6 segments et remonter

- N : 10 → 6 segments (garder les 6 du bas, plus fins)
- pyr_h : 90 → 54 pixels (proportionnel, même hauteur segment)
- margin_top : 10 → 6 pixels (remonte la pyramide)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VmaVcCrWp2QG7hkEDk15Cv

receive_cam.py

@@ -137,11 +137,11 @@ def draw_rssi_pyramid(frame: np.ndarray) -> np.ndarray:
         rssi = _rssi_data
 
     h, w = frame.shape[:2]
-    N = 10
+    N = 6
     pyr_w = 70
-    pyr_h = 90
+    pyr_h = 54
     gap = 2
-    margin_top = 10
+    margin_top = 6
     margin_right = 10
     x_center = w - margin_right - pyr_w // 2
     y_top = margin_top