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_clear_simple_collision.py

@@ -0,0 +1,66 @@
+"""Remove the auto-generated simple collision from the site meshes, keeping their triangles.
+
+    <engine>/UnrealEditor-Cmd <uproject> -run=pythonscript \
+        -script=<repo>/Tools/unreal/ue_clear_simple_collision.py -nullrhi -unattended -nopause -stdout
+
+Why: the FBX import runs with `auto_generate_collision`, which adds ONE convex hull per mesh. For a
+279 m terrain or road that hull is a giant slab, and any *physics body* inside it - the Chaos vehicle -
+is pushed out of the hull every frame. Walked characters never notice, because character movement
+sweeps instead of resolving penetration, which is why the player was fine while the car was thrown
+into the air.
+
+Clearing the hulls leaves `CTF_USE_COMPLEX_AS_SIMPLE`, so traces and physics use the real triangles.
+
+Result: /tmp/gigline/clear-simple-collision.txt
+"""
+
+import unreal
+
+FOLDERS = ("/Game/Hollywood/Site", "/Game/Hollywood/Streets")
+RESULT = "/tmp/gigline/clear-simple-collision.txt"
+lines = []
+
+
+def log(message):
+    lines.append(str(message))
+    unreal.log(str(message))
+
+
+def main():
+    cleared = 0
+    for folder in FOLDERS:
+        for path in unreal.EditorAssetLibrary.list_assets(folder, recursive=False):
+            mesh = unreal.EditorAssetLibrary.load_asset(path)
+            if not isinstance(mesh, unreal.StaticMesh):
+                continue
+            body = mesh.get_editor_property("body_setup")
+            if body is None:
+                continue
+            agg = body.get_editor_property("agg_geom")
+            convex = len(agg.get_editor_property("convex_elems"))
+            boxes = len(agg.get_editor_property("box_elems"))
+            if not convex and not boxes:
+                continue
+            agg.set_editor_property("convex_elems", [])
+            agg.set_editor_property("box_elems", [])
+            body.set_editor_property("agg_geom", agg)
+            body.set_editor_property("collision_trace_flag",
+                                     unreal.CollisionTraceFlag.CTF_USE_COMPLEX_AS_SIMPLE)
+            mesh.set_editor_property("body_setup", body)
+            unreal.EditorAssetLibrary.save_loaded_asset(mesh)
+            log(f"{mesh.get_name()}: cleared {convex} convex, {boxes} box, complex-as-simple")
+            cleared += 1
+    lines.append(f"VERDICT: {'PASS' if cleared else 'NOTHING-TO-DO'}")
+    log(f"{cleared} meshes cleared")
+
+
+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")