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_vehicle_probe_map.py

@@ -0,0 +1,111 @@
+"""Add one piece of demo content to ReviewMap and save it as a vehicle probe level.
+
+    GIGLINE_PROBE_ASSET=Terrain_DEM [GIGLINE_PROBE_NOCOLLISION=1] <engine>/UnrealEditor-Cmd <uproject> \
+        -run=pythonscript -script=<repo>/Tools/unreal/ue_vehicle_probe_map.py -nullrhi -unattended -nopause
+
+Why: the Chaos pawn falls correctly on ReviewMap's empty floor and is thrown upward everywhere in
+DemoMap. Rather than guess which of DemoMap's 593 staged meshes is responsible, add them one group
+at a time to the map that works and watch for the moment the pawn stops falling. With no
+GIGLINE_PROBE_ASSET set, the level is a plain copy of ReviewMap - the control.
+
+Assets are looked up as /Game/Hollywood/Site/<name> first, then /Game/Hollywood/Buildings/<name>.
+Result: /tmp/gigline/vehicle-probe.txt
+"""
+
+import os
+
+import unreal
+
+RESULT = "/tmp/gigline/vehicle-probe.txt"
+TARGET = "/Game/Test/VehicleProbe"
+SOURCE = "/Game/Test/ReviewMap"
+SEARCH = ("/Game/Hollywood/Site", "/Game/Hollywood/Buildings",
+          "/Game/Hollywood/Streets", "/Game/Hollywood/Props")
+lines = []
+
+
+def log(message):
+    lines.append(str(message))
+    unreal.log(str(message))
+
+
+def find_asset(name):
+    for folder in SEARCH:
+        path = f"{folder}/{name}"
+        if unreal.EditorAssetLibrary.does_asset_exist(path):
+            return path
+    return None
+
+
+def main():
+    wanted = os.environ.get("GIGLINE_PROBE_ASSET", "").strip()
+    if not unreal.EditorAssetLibrary.does_asset_exist(SOURCE):
+        log(f"missing source level {SOURCE}")
+        lines.append("VERDICT: FAIL")
+        return
+    target = TARGET
+    # A level that the previous run left behind cannot always be deleted while the editor holds it,
+    # so fall back to a suffixed name rather than failing the probe.
+    for suffix in ("", "_b", "_c", "_d"):
+        target = TARGET + suffix
+        if not unreal.EditorAssetLibrary.does_asset_exist(target):
+            break
+        unreal.EditorAssetLibrary.delete_asset(target)
+        if not unreal.EditorAssetLibrary.does_asset_exist(target):
+            break
+    if not unreal.EditorAssetLibrary.duplicate_asset(SOURCE, target):
+        log(f"could not duplicate {SOURCE} -> {TARGET}")
+        lines.append("VERDICT: FAIL")
+        return
+    log(f"duplicated {SOURCE} -> {target}")
+    unreal.EditorLevelLibrary.load_level(target)
+
+    if wanted:
+        path = find_asset(wanted)
+        if path is None:
+            log(f"MISSING asset {wanted} in {SEARCH}")
+            lines.append("VERDICT: FAIL")
+            return
+        mesh = unreal.EditorAssetLibrary.load_asset(path)
+        actor = unreal.EditorLevelLibrary.spawn_actor_from_class(
+            unreal.StaticMeshActor, unreal.Vector(0.0, 0.0, 0.0))
+        comp = actor.get_component_by_class(unreal.StaticMeshComponent)
+        comp.set_static_mesh(mesh)
+        actor.set_actor_label(f"Probe_{wanted}")
+        log(f"staged probe mesh {path} at the origin")
+        # GIGLINE_PROBE_NOCOLLISION=1 stages the same mesh with no collision at all, which separates
+        # "this mesh's collision ejects physics bodies" from "this mesh does something else".
+        if os.environ.get("GIGLINE_PROBE_NOCOLLISION", "").strip() == "1":
+            comp.set_collision_enabled(unreal.CollisionEnabled.NO_COLLISION)
+            log("probe mesh collision disabled")
+    else:
+        log("control run: no extra content")
+
+    vehicle_class = unreal.load_class(None, "/Script/GigLine.GigLineVehicle")
+    if vehicle_class:
+        pawn = unreal.EditorLevelLibrary.spawn_actor_from_class(
+            vehicle_class, unreal.Vector(600.0, 0.0, 300.0))
+        pawn.set_actor_label("Probe_Vehicle")
+        log("staged the Chaos pawn at (600, 0, 300)")
+    else:
+        log("vehicle class not found")
+
+    if unreal.EditorLevelLibrary.save_current_level():
+        log(f"saved {target}")
+        lines.append(f"LEVEL: {target}")
+        lines.append("VERDICT: PASS")
+    else:
+        log(f"save failed for {target}")
+        lines.append("VERDICT: FAIL")
+
+
+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")
+
+with open(RESULT, "w") as f:
+    f.write("\n".join(lines) + "\n")