sar3d: GPU port of the notebook with four views

The sar3d processor is rewritten as a checked port of Multi_antenna_3D_clean_v1.ipynb:
NVRTC kernels, timing from the trace stamps, notebook parameter names and one cubic
SAR_VOXEL_M. It adds front, side, top and 3D views, drops gpr_cpp and the parity tools,
and the GUI speed now applies only while the socket speed is ignored.

start.sh

@@ -133,10 +133,27 @@ except Exception:
     echo "[start.sh] Detected radar model: ${RADAR_MODEL} (config: ${config_path})"
 }
 
+# radar.replay.dataset_dir of a config, empty unless it replays a recording.
+replay_dataset_dir() {
+    python3 -c '
+import json, sys
+try:
+    radar = json.load(open(sys.argv[1])).get("radar", {})
+    print(str(radar.get("replay", {}).get("dataset_dir", "")).strip())
+except Exception:
+    print("")
+' "$1" 2>/dev/null
+}
+
 # Acquisition producer for the active model, mirroring the process supervisor's
-# selection so --producer-only behaves identically to a full pipeline launch.
+# selection so --producer-only behaves identically to a full pipeline launch: a
+# replay dataset takes precedence over the model's producer.
 producer_command() {
     local config_path="$1"
+    if [[ -n "$(replay_dataset_dir "${config_path}")" ]]; then
+        printf '%s\0' "${PYTHON_CMD}" -m python_app.scripts.replay_raw_producer --config "${config_path}"
+        return
+    fi
     case "${RADAR_MODEL}" in
         kamil_adc)
             printf '%s\0' "${PYTHON_CMD}" -m python_app.scripts.kamil_adc_raw_producer --config "${config_path}" ;;
@@ -244,7 +261,7 @@ ensure_system_dependencies() {
         return
     fi
 
-    echo "[start.sh] Installing system dependency: libusb-1.0 dev headers..."
+    echo "[start.sh] Installing system dependencies: libusb-1.0 dev headers (and Qt xcb libraries on apt)..."
     if command -v apt-get >/dev/null 2>&1; then
         run_privileged apt-get update
         run_privileged apt-get install -y pkg-config libusb-1.0-0-dev libxcb-cursor0 libxkbcommon-x11-0