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/figures/F8_attention_combined.py

@@ -0,0 +1,72 @@
+"""F8 combined explainability panel: disc-centred attention + quadrant breakdown.
+
+Composes a single A/B figure from two existing renderings:
+    A: ``F8_gradcam/disc_attention_detail.png`` — 2x2 grid of mean Grad-CAM
+       heatmaps for {correct, incorrect} x {Normal, Glaucoma} cells, with the
+       mean disc boundary annotated as a dashed circle.
+    B: ``F8_quadrant_attention.png`` — grouped-bar chart of mean full-image
+       Grad-CAM fraction per optic-disc quadrant, by cell.
+
+Both source panels are produced by ``v4.figures.F8_explainability`` and
+``v4.figures.F8_quadrant_plot`` respectively; this script just stitches the
+two PNGs into a single combined figure with A/B subfigure labels.
+
+Re-run:
+    python -m v4.figures.F8_attention_combined
+"""
+from __future__ import annotations
+
+from pathlib import Path
+
+import matplotlib
+matplotlib.use("Agg")
+import matplotlib.pyplot as plt
+from PIL import Image
+
+
+SRC_A = Path(__file__).parent / "output" / "F8_gradcam" / "disc_attention_detail.png"
+SRC_B = Path(__file__).parent / "output" / "F8_quadrant_attention.png"
+OUT   = Path(__file__).parent / "output" / "F8_attention_combined.png"
+
+
+def render() -> None:
+    for p in (SRC_A, SRC_B):
+        if not p.exists():
+            raise SystemExit(
+                f"Source panel missing: {p}\n"
+                "Run F8_explainability (for A) and F8_quadrant_plot (for B) first."
+            )
+
+    img_a = Image.open(SRC_A)
+    img_b = Image.open(SRC_B)
+
+    # Stack vertically: A on top (square), B below (wider).
+    fig = plt.figure(figsize=(13.0, 13.6))
+    gs = fig.add_gridspec(
+        2, 1,
+        height_ratios=[img_a.size[1] / img_a.size[0],
+                       img_b.size[1] / img_b.size[0] * 13.0 / 13.0],
+        hspace=0.06,
+    )
+
+    ax_a = fig.add_subplot(gs[0])
+    ax_a.imshow(img_a)
+    ax_a.axis("off")
+    ax_a.text(-0.01, 1.01, "A", transform=ax_a.transAxes,
+              ha="left", va="bottom", fontsize=22, fontweight="bold")
+
+    ax_b = fig.add_subplot(gs[1])
+    ax_b.imshow(img_b)
+    ax_b.axis("off")
+    ax_b.text(-0.01, 1.01, "B", transform=ax_b.transAxes,
+              ha="left", va="bottom", fontsize=22, fontweight="bold")
+
+    fig.tight_layout()
+    OUT.parent.mkdir(parents=True, exist_ok=True)
+    fig.savefig(OUT, dpi=180, bbox_inches="tight")
+    plt.close(fig)
+    print(f"saved {OUT}")
+
+
+if __name__ == "__main__":
+    render()