refactor(tools): group the sixty scripts by what they talk to

One directory with sixty scripts stopped being navigable, and the grouping is also the sandbox boundary:

  Tools/unreal/    commandlets and the two map builders, with ue_common.py and ue_placement.py as the
                   shared imports (they need the engine)
  Tools/blender/   builders, exporters, the FBX preset, the MPFB character pipeline, blender_screenshots
                   (they need the Blender Flatpak)
  Tools/review/    the visual loop: render_screenshots.sh, judge_screenshot.py, hero_compare.py,
                   build_comparison_md.py, e2e_asset_check.py, hero_iterate.sh, visual_loop.py,
                   visual_targets.json
  Tools/gen/       image and texture generation: the ComfyUI driver, deterministic texture writers,
                   reference fetching
  Tools/input/     OS-level input injection
  root             _common.py, check-lfs.sh, addon_compat_probe.py, sibling_asset_audit.py, tests/

Every moved script now resolves the repository root as ../.. and puts the tools root plus its siblings on
sys.path, so 'import ue_common' still works from unreal/. The test suite bootstrap does the same for the five
folders. render_screenshots.sh takes the folder as a third argument to run_cmdlet, and the e2e driver,
hero_iterate.sh and the comparison generator were repointed.

51 README rows now link to their new location, the README gains a Layout section naming each folder's
sandbox, and the architecture notes and Blender README follow the moves.

Verified: 108 tests pass, prettier is clean, judge_screenshot.py and hero_compare.py run from their new
homes, and the e2e run was aborted mid-way (it had been rebuilding an empty DemoMap for 15 minutes) and is
being rerun against the new layout.

Tools/blender/scale_test_export.py

@@ -0,0 +1,71 @@
+# Scale-test scene builder and FBX exporter for the Blender -> Unreal pipeline.
+#
+# Builds three 1 m cubes in the project geographic frame (EPSG:26911, origin
+# Hollywood x Highland, X east / Y north / Z up):
+#   ScaleTest_A  centred at (0, 0, 0.5)      - origin + 1 m size reference
+#   ScaleTest_B  centred at (10, 0, 0.5)     - +10 m east probe
+#   ScaleTest_C  centred at (0, 10, 0.5)     - +10 m north probe
+# and exports them as one FBX with the named export preset "ue_metric_v1".
+#
+# Run headless (see Art/blender/README.md for the Flatpak invocation):
+#   blender -b --factory-startup --python Tools/blender/scale_test_export.py -- \
+#     --out /tmp/gigline/scaletest.fbx --save-blend Art/blender/scaletest/scale-test-<date>.blend
+
+import argparse
+import os
+import sys
+
+import bpy
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+import fbx_export_preset as fbx_preset  # noqa: E402
+
+
+
+def build_scene():
+    scene = bpy.context.scene
+    for obj in list(bpy.data.objects):
+        bpy.data.objects.remove(obj, do_unlink=True)
+
+    mat = bpy.data.materials.new("M_ScaleTest_Red")
+    mat.use_nodes = True
+    bsdf = mat.node_tree.nodes.get("Principled BSDF")
+    bsdf.inputs["Base Color"].default_value = (0.8, 0.05, 0.05, 1.0)
+
+    specs = {
+        "ScaleTest_A": (0.0, 0.0, 0.5),
+        "ScaleTest_B": (10.0, 0.0, 0.5),
+        "ScaleTest_C": (0.0, 10.0, 0.5),
+    }
+    for name, loc in specs.items():
+        bpy.ops.mesh.primitive_cube_add(size=1.0, location=loc)
+        obj = bpy.context.active_object
+        obj.name = name
+        obj.data.materials.append(mat)
+        print(f"[scale_test] created {name} at {loc}")
+
+
+def export_fbx(path):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    # Named export preset "ue_metric_v1" - change only via a new preset name.
+    fbx_preset.export_static(path)
+    print(f"[scale_test] exported FBX preset ue_metric_v1 -> {path}")
+
+
+def main():
+    argv = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else []
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--out", default="/tmp/gigline/scaletest.fbx")
+    parser.add_argument("--save-blend", default=None)
+    args = parser.parse_args(argv)
+
+    build_scene()
+
+    if args.save_blend:
+        os.makedirs(os.path.dirname(args.save_blend), exist_ok=True)
+        bpy.ops.wm.save_as_mainfile(filepath=args.save_blend)
+        print(f"[scale_test] saved {args.save_blend}")
+
+    export_fbx(args.out)
+
+
+main()