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/unreal/ue_character_import.py

@@ -0,0 +1,117 @@
+# Unreal-side half of the MPFB character acceptance: imports the skeletal FBX
+# with the named import preset "ue_character_v1" and verifies the result.
+#
+#   UnrealEditor-Cmd <uproject> -run=pythonscript -script=<repo>/Tools/unreal/ue_character_import.py \
+#     -nullrhi -unattended -nopause -stdout
+
+import unreal
+
+FBX = "/tmp/gigline/character.fbx"
+DEST = "/Game/Test/Character"
+REPORT = "/tmp/ue-character-result.txt"
+lines = []
+
+
+def log(msg):
+    lines.append(str(msg))
+
+
+def import_character():
+    if unreal.EditorAssetLibrary.does_directory_exist(DEST):
+        unreal.EditorAssetLibrary.delete_directory(DEST)
+    task = unreal.AssetImportTask()
+    task.filename = FBX
+    task.destination_path = DEST
+    task.automated = True
+    task.save = True
+    task.replace_existing = True
+
+    ui = unreal.FbxImportUI()
+    ui.import_mesh = True
+    ui.import_materials = True
+    ui.import_textures = True
+    ui.import_as_skeletal = True
+    ui.import_animations = False
+
+    smd = ui.skeletal_mesh_import_data
+    smd.import_uniform_scale = 1.0
+    smd.convert_scene_unit = False
+    smd.force_front_x_axis = False
+    smd.normal_import_method = unreal.FBXNormalImportMethod.FBXNIM_IMPORT_NORMALS
+    task.options = ui
+
+    unreal.AssetToolsHelpers.get_asset_tools().import_asset_tasks([task])
+    unreal.EditorLoadingAndSavingUtils.save_dirty_packages(True, True)
+
+
+def import_texture_and_material():
+    # Interchange 5.8 does not create material/texture assets for skeletal
+    # FBX imports; finish the baked-material chain explicitly.
+    task = unreal.AssetImportTask()
+    task.filename = "/tmp/gigline/T_Character_Diffuse.png"
+    task.destination_path = DEST
+    task.automated = True
+    task.save = True
+    task.replace_existing = True
+    unreal.AssetToolsHelpers.get_asset_tools().import_asset_tasks([task])
+
+    tex = unreal.EditorAssetLibrary.load_asset(f"{DEST}/T_Character_Diffuse")
+    log(f"texture: {tex.get_class().get_name() if tex else 'MISSING'}")
+
+    mat_path = f"{DEST}/M_Character_Export"
+    if unreal.EditorAssetLibrary.does_asset_exist(mat_path):
+        unreal.EditorAssetLibrary.delete_asset(mat_path)
+    mat = unreal.AssetToolsHelpers.get_asset_tools().create_asset(
+        "M_Character_Export", DEST, unreal.Material, unreal.MaterialFactoryNew())
+    tex_expr = unreal.MaterialEditingLibrary.create_material_expression(
+        mat, unreal.MaterialExpressionTextureSample)
+    tex_expr.set_editor_property("texture", tex)
+    unreal.MaterialEditingLibrary.connect_material_property(
+        tex_expr, "RGB", unreal.MaterialProperty.MP_BASE_COLOR)
+    unreal.MaterialEditingLibrary.recompile_material(mat)
+
+    sm = unreal.EditorAssetLibrary.load_asset(f"{DEST}/character")
+    entry = unreal.SkeletalMaterial()
+    entry.set_editor_property("material_interface", mat)
+    entry.set_editor_property("material_slot_name", "M_Character_Export")
+    sm.set_editor_property("materials", [entry])
+    unreal.EditorAssetLibrary.save_loaded_asset(sm)
+    log("material assigned to slot 0 (via SkeletalMaterial.material_interface)")
+    unreal.EditorLoadingAndSavingUtils.save_dirty_packages(True, True)
+
+
+def verify():
+    sm = unreal.EditorAssetLibrary.load_asset(f"{DEST}/character")
+    if sm is None:
+        log(f"MISSING skeletal asset {DEST}/character; assets: {unreal.EditorAssetLibrary.list_assets(DEST)}")
+        return
+    log(f"class: {sm.get_class().get_name()}")
+    try:
+        skel = sm.get_editor_property("skeleton")
+        tree = skel.get_editor_property("bone_tree")
+        log(f"bones: {len(tree)}")
+    except Exception as exc:  # noqa
+        log(f"bone count unavailable: {exc!r}")
+    try:
+        mats = sm.get_editor_property("materials")
+        log(f"material slots: {len(mats)} -> {[m.get_editor_property('material_slot_name') for m in mats]}")
+    except Exception as exc:  # noqa
+        log(f"material slots unavailable: {exc!r}")
+    try:
+        bounds = sm.get_editor_property("bounds")
+        o, e = bounds.origin, bounds.box_extent
+        log(f"bounds cm: size=({e.x * 2:.1f}, {e.y * 2:.1f}, {e.z * 2:.1f}) origin=({o.x:.1f}, {o.y:.1f}, {o.z:.1f})")
+    except Exception as exc:  # noqa
+        log(f"bounds unavailable: {exc!r}")
+    log(f"assets: {unreal.EditorAssetLibrary.list_assets(DEST)}")
+    # materials actually imported as assets?
+    for a in unreal.EditorAssetLibrary.list_assets(DEST):
+        obj = unreal.EditorAssetLibrary.load_asset(a)
+        log(f"  {a} : {obj.get_class().get_name()}")
+
+
+import_character()
+import_texture_and_material()
+verify()
+with open(REPORT, "w") as f:
+    f.write("\n".join(lines) + "\n")