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/10_quality_requirements.md

@@ -22,7 +22,7 @@ Ordered by priority: realism first, performance last. The order decides design t
 
 | ID | Source/Stimulus | Response | Metric |
 | --- | --- | --- | --- |
-| QS-1 | Screenshot is compared against its reference photograph | The render reads as the same building | Similarity score and visual match confirmed by the owner; `Tools/visual_loop.py` reports the deltas |
+| QS-1 | Screenshot is compared against its reference photograph | The render reads as the same building | Similarity score and visual match confirmed by the owner; `Tools/review/visual_loop.py` reports the deltas |
 | QS-2 | A façade is placed from measured data | It sits on its verified footprint | World span probed against `Geo/verification/` within ~1 m |
 | QS-3 | Player walks both sides of the demo | No fall-through, character stays at ground Z | 0 raycast holes in 84-sample transect |
 | QS-4 | Player holds W for 2 s on flat road | Character moves forward | ≥ 200 cm displacement, Z constant within ±5 cm |
@@ -41,5 +41,5 @@ Ordered by priority: realism first, performance last. The order decides design t
 | BR-1 | A building with a reference photograph has a review shot compared against it | Silhouette and proportion deltas recorded per building in `Screenshots/README.md`; owner approval per shot |
 | BR-2 | Every building is either photo-matched or explicitly recorded as an unfounded blockout | List in `TODO.md`; no building in an in-between state |
 | BR-3 | Every building has a collision proxy and at least one LOD | Count of buildings missing either = 0 |
-| BR-4 | No surface carries a placeholder material | Material audit in `Tools/ue_audit_scene.py` reports 0 placeholder slots |
+| BR-4 | No surface carries a placeholder material | Material audit in `Tools/unreal/ue_audit_scene.py` reports 0 placeholder slots |
 | BR-5 | The realism pass does not break the floor | QS-9 still holds at 1440p, with the measured cost of the pass recorded |