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_clothing_import.py

@@ -0,0 +1,71 @@
+# Import the garment meshes as separate skeletal meshes (0.2.2).
+#
+#   blender -b Art/blender/character/character-2026-11-07.blend \
+#       --python Tools/blender/character_clothing_build.py -- --out /tmp/gigline/clothing
+#   <engine>/Engine/Binaries/Linux/UnrealEditor-Cmd <uproject> -run=pythonscript \
+#     -script=<repo>/Tools/unreal/ue_character_clothing_import.py -nullrhi -unattended -nopause -stdout
+#
+# Each garment is its own asset, per the character-artist skill's rule that clothing
+# stays separate so it can be swapped or re-materialled. The pawn attaches each one as
+# a component using the body as the leader pose.
+#
+# Result file: /tmp/gigline/character-clothing-import.txt
+
+import unreal
+
+DEST = "/Game/Test/Character"
+SOURCE = "/tmp/gigline/clothing"
+GARMENTS = (("tee", "CharacterTee"), ("jeans", "CharacterJeans"), ("shoes", "CharacterShoes"))
+RESULT = "/tmp/gigline/character-clothing-import.txt"
+lines = []
+
+
+def log(msg):
+    lines.append(str(msg))
+    unreal.log(str(msg))
+
+
+def main():
+    for source, name in GARMENTS:
+        task = unreal.AssetImportTask()
+        task.filename = f"{SOURCE}/{source}.fbx"
+        task.destination_path = DEST
+        task.destination_name = name
+        task.automated = True
+        task.save = True
+        task.replace_existing = True
+
+        ui = unreal.FbxImportUI()
+        ui.import_mesh = True
+        ui.import_as_skeletal = True
+        ui.import_animations = False
+        ui.import_materials = True
+        ui.import_textures = False
+        ui.skeletal_mesh_import_data.import_uniform_scale = 1.0
+        task.options = ui
+        unreal.AssetToolsHelpers.get_asset_tools().import_asset_tasks([task])
+
+        mesh = unreal.EditorAssetLibrary.load_asset(f"{DEST}/{name}")
+        if mesh is None:
+            log(f"{name}: MISSING after import")
+            lines.append("VERDICT: FAIL")
+            return
+        mats = mesh.get_editor_property("materials")
+        log(f"{name}: imported, {len(mats)} slot(s): "
+            + ", ".join((m.get_editor_property("material_interface").get_name()
+                         if m.get_editor_property("material_interface") else "None")
+                        for m in mats))
+    lines.append("VERDICT: PASS")
+
+
+try:
+    main()
+except Exception as exc:  # noqa: BLE001
+    import traceback
+    log(f"FAILED: {type(exc).__name__}: {exc}")
+    log(traceback.format_exc())
+    lines.append("VERDICT: FAIL")
+
+unreal.EditorLoadingAndSavingUtils.save_dirty_packages(True, True)
+with open(RESULT, "w") as f:
+    f.write("\n".join(lines) + "\n")