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.

Docs/Architecture/06_runtime_view.md

@@ -18,7 +18,7 @@
 
 ## Screenshot capture
 
-1.  `Tools/render_screenshots.sh` compiles editor, builds `ReviewMap` from `Tools/ue_build_review_map.py`, launches game in `-game` mode.
+1.  `Tools/review/render_screenshots.sh` compiles editor, builds `ReviewMap` from `Tools/unreal/ue_build_review_map.py`, launches game in `-game` mode.
 
 2.  `AGigLineShotActor` iterates the camera list, sets view, calls `HighResShot 1280x720`, waits for capture.
 
@@ -48,6 +48,6 @@
 
 1.  Blender headless (`Tools/export_*.py`) reads `.blend` files, applies metre→centimetre conversion, exports FBX with `ue_metric_v1` preset.
 
-2.  Unreal headless (`Tools/ue_import_*.py`) imports FBX via Interchange, places meshes at geographic coordinates, sets collision profiles.
+2.  Unreal headless (`Tools/unreal/ue_import_*.py`) imports FBX via Interchange, places meshes at geographic coordinates, sets collision profiles.
 
-3.  `Tools/ue_build_demo_map.py` assembles `DemoMap`: creates/repositions actors, sets lighting, saves map and assets.
+3.  `Tools/unreal/ue_build_demo_map.py` assembles `DemoMap`: creates/repositions actors, sets lighting, saves map and assets.