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/review/visual_targets.json

@@ -0,0 +1,137 @@
+{
+  "comment": "What each demo-map capture must show, and which reference photograph it is measured against. Used by Tools/visual_loop.py --verify (does the shot show the expected content?) and --compare (how far is the render from the reference?).",
+  "targets": [
+    {
+      "name": "demo-spawn-view",
+      "shot": "Screenshots/demo/review-demo-spawn-view.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
+      ],
+      "expect": "A daytime street view from the north sidewalk: a light-coloured neoclassical facade with columns across the road, a red car and a walking person on the pavement, road in the foreground Nothing may float: the person's feet and the car's wheels must meet the pavement and their shadows must touch them. A shadow on the ground more than a hand's width below an object means the object is floating."
+    },
+    {
+      "name": "demo-street-level",
+      "shot": "Screenshots/demo/review-demo-street-level.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-theatre-blade-sign-day-wikimedia-2008-10.jpg"
+      ],
+      "expect": "Street level looking along the road: a colonnade of columns with a light facade above, pavement and road visible, daylight, no floating geometry"
+    },
+    {
+      "name": "demo-crossing",
+      "shot": "Screenshots/demo/review-demo-crossing.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/walk-of-fame-terrazzo-ovation-day-cc0-2019-06-20.jpg"
+      ],
+      "expect": "A road surface with white crossing markings, a light-coloured building frontage behind, daylight"
+    },
+    {
+      "name": "demo-north-buildings",
+      "shot": "Screenshots/demo/review-demo-north-buildings.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/north-chinese/01-grauman-s-chinese-theatre-by-carol-highsmith.jpg"
+      ],
+      "expect": "Tall light-grey building masses along the street on both sides, seen from road level, daylight, no missing faces or floating parts"
+    },
+    {
+      "name": "demo-retail-frontage",
+      "shot": "Screenshots/demo/review-demo-retail-frontage.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/retail-neighbours/01-lee-drug-and-neighbor.jpg"
+      ],
+      "expect": "A row of light shopfront facades with dark openings at street level, seen from across the road, daylight"
+    },
+    {
+      "name": "demo-third-person",
+      "shot": "Screenshots/demo/review-demo-third-person.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
+      ],
+      "expect": "A third-person view of a clothed human character standing on a pavement, seen from behind, a large building facade across the road"
+    },
+    {
+      "name": "demo-third-person-front",
+      "shot": "Screenshots/demo/review-demo-third-person-front.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
+      ],
+      "expect": "A clothed human character standing on a pavement seen from the front, dark navy top and dark trousers, light building behind, daylight"
+    },
+    {
+      "name": "demo-third-person-walk",
+      "shot": "Screenshots/demo/review-demo-third-person-walk.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/reference/hollywood/el-capitan-facade-day-wikimedia-2009-10-27.jpg"
+      ],
+      "expect": "A clothed human character walking along a pavement, legs apart in mid-stride, seen from the side, daylight"
+    },
+    {
+      "name": "demo-vehicle",
+      "shot": "Screenshots/demo/review-demo-vehicle.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Art/blender/vehicle/hatch-reference.png"
+      ],
+      "expect": "A red compact hatchback car parked on a pavement beside a person, with dark windows, four dark wheels and a dark bumper, daytime"
+    },
+    {
+      "name": "demo-feet",
+      "shot": "Screenshots/demo/review-demo-feet.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Screenshots/blender/character-angle-035.png"
+      ],
+      "expect": "Low view of a person's feet standing on a pavement, seen along the ground, daylight. The object must touch the surface: feet or wheels in contact, with the shadow starting at that contact point, not on the ground far below."
+    },
+    {
+      "name": "demo-wheel",
+      "shot": "Screenshots/demo/review-demo-wheel.png",
+      "size": [
+        1920,
+        1080
+      ],
+      "references": [
+        "Screenshots/blender/vehicle-angle-035.png"
+      ],
+      "expect": "Low view of a car's wheels standing on a pavement, seen along the ground, daylight. The object must touch the surface: feet or wheels in contact, with the shadow starting at that contact point, not on the ground far below."
+    }
+  ]
+}