fix: clés JSON sideband alignées sur payload Pi Zero

temp → temp_c, cpu → cpu_pct pour correspondre exactement
au format {ts, width, height, fps, encoder, bitrate_kbps,
temp_c, cpu_pct, throttled, uptime_s} émis par le Pi Zero.

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

receive_cam.py

@@ -81,8 +81,8 @@ def draw_overlay(frame: np.ndarray) -> np.ndarray:
     h_res   = stats.get("height", "?")
     fps     = stats.get("fps", "?")
     enc     = stats.get("encoder", "?")
-    temp    = stats.get("temp", "?")
-    cpu     = stats.get("cpu", "?")
+    temp    = stats.get("temp_c", "?")
+    cpu     = stats.get("cpu_pct", "?")
     throttled = stats.get("throttled", False)
     throttle_str = "THROTTLED" if throttled else "ok"