Add analysis scripts and experiment configurations for bridge attention and sensitivity studies

- Introduced `bridge_attention_ceiling_check.py` for variance decomposition analysis on bridge attention configurations.
- Added `bridge_attention_readout.py` to perform per-tower gate and contribution readouts, including AUC sanity checks.
- Created multiple JSON configuration files for backbone replication experiments, including anonymous CV variants and basic backbones.
- Implemented sensitivity experiments to evaluate the impact of axial length inclusion and EfficientNetV2-M performance at higher resolutions.
- Added a memory probe script to assess GPU memory usage during training with EfficientNetV2-M.

v4/scripts/experiments/backbone_replication/anonymous_cv.json

@@ -0,0 +1,10 @@
+[
+  {
+    "_note": "F2 block 2 — Anonymous CV variant of the refugelike R50 image-only single-eye baseline. split_identity_level=0 disables patient-level fold grouping (v4_hypertower.py:254-256); fold assignment becomes patient-anonymous, allowing the two eyes of one patient to fall on opposite sides of the train/test split. Mirrors v3 phase 2 imageonly_resnet50_leaky. Same backbone, same architecture, same seed/fold_seed as the F2 block-3 baseline (refugelike img-only single-eye); only the grouping rule changes. The gap baseline→anonymous quantifies the patient-anonymous CV inflation.",
+    "run_name": "experiments/backbone_replication/anonymous_cv_refugelike",
+    "reps": 10,
+    "overrides": {
+      "split_identity_level": 0
+    }
+  }
+]