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/04_solution_strategy.md

@@ -30,7 +30,7 @@ All modelling and geographic processing live outside the game project in `Art/`,
 
 ## Quality achievement
 
-- **Realism first**: reference photography and measured data drive every façade decision; renders are compared against the photographs with `Tools/visual_loop.py`, and a façade is built from the shared 4.96 m module kit so the street wall reads consistently. Materials are authored in Unreal with world-aligned generated textures, and lighting is fixed daytime so a shot is comparable between runs.
+- **Realism first**: reference photography and measured data drive every façade decision; renders are compared against the photographs with `Tools/review/visual_loop.py`, and a façade is built from the shared 4.96 m module kit so the street wall reads consistently. Materials are authored in Unreal with world-aligned generated textures, and lighting is fixed daytime so a shot is comparable between runs.
 - **Performance as a budget, not a driver**: dynamic-only lighting (no build step, no static shadow maps), world-space-noise materials (cheap procedural variation), minimal overdraw for street-level geometry, and a 60 FPS at 1440p floor that every release must meet. It closes the quality list because it constrains how much realism fits, not what the block should look like.
 
 - **Walkability**: complex-as-simple collision on terrain (C++ helper forces the flag on the asset), block-all collision on every site mesh, swept transect QA verifies zero raycast holes.