Add reduced gold 4D-STEM tutorial dataset

4dstem/gold_128_npy_bin8/data.npy

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+version https://git-lfs.github.com/spec/v1
+oid sha256:a9c78651ad841de042db214700a63af31e298c35b295d83d8347980643be3fd2
+size 18874496

4dstem/gold_128_npy_bin8/meta.json

@@ -0,0 +1,53 @@
+{
+  "name": "gold_128_npy_bin8",
+  "shape": [
+    128,
+    128,
+    24,
+    24
+  ],
+  "dtype": "uint16",
+  "sampling": [
+    2.0,
+    2.0,
+    3.68,
+    3.68
+  ],
+  "units": [
+    "A",
+    "A",
+    "mrad",
+    "mrad"
+  ],
+  "bin_factor": {
+    "scan": 4,
+    "det": 8
+  },
+  "original_shape": [
+    512,
+    512,
+    192,
+    192
+  ],
+  "original_sampling": [
+    0.5,
+    0.5,
+    0.46,
+    0.46
+  ],
+  "source": "Arina 4D-STEM master /home/owner/ssd/data/bob/20260423_gold_drift_v6_4dstem_pair/gold_004_master.h5 (drift-pair acquisition; sibling session 20260408_gold_4dstem_512_ssb/dataset.yaml supplies optics)",
+  "purpose": "workshop / Colab demo - reduced real-space scan, detector-only bin8 source",
+  "voltage_kV": 300,
+  "camera_length_mm": 91,
+  "probe_semiangle_mrad": 30,
+  "mag_MX": null,
+  "rotation_deg": 0.0,
+  "voltage_kV_source": "confirmed via session HAADF EMD (20260423/0072-*.emd, AccelerationVoltage)",
+  "probe_semiangle_source": "confirmed via session HAADF EMD (BeamConvergence 0.02999 rad)",
+  "camera_length_source": "confirmed via session HAADF EMD (CameraLength 0.091 m)",
+  "scan_sampling_A_source": "operator pattern from sibling 20260408 SSB calibration.json; not per-file calibrated for this 20260423 drift acquisition",
+  "survey_haadf_mag_MX": 2.6,
+  "survey_haadf_fov_nm": 38.1,
+  "source_dataset": "4dstem/gold_512_npy_bin8",
+  "processing": "real-space 4x4 block average from gold_512_npy_bin8; detector remains bin8"
+}