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/controls.md

@@ -19,7 +19,7 @@ Keyboard and mouse. The same list is shown in-game, bottom-right of the frame (`
 
 - Movement is relative to where you are looking (controller yaw), so the capsule stays upright on the sloped street.
 - The mouse is captured on launch, so looking works without clicking first. `Escape` toggles the capture as part of pause.
-- Bindings are Enhanced Input actions in `/Game/Input` built by `Tools/ue_create_input_assets.py`; the mapping context is `IMC_Default`.
+- Bindings are Enhanced Input actions in `/Game/Input` built by `Tools/unreal/ue_create_input_assets.py`; the mapping context is `IMC_Default`.
 
 ## Changes since `0.1.0`
 
@@ -48,10 +48,10 @@ The walking shot is driven per shot rather than by the switch: the shot actor en
 
 ## Testing input without a physical keyboard
 
-`Tools/input_test.py` injects OS-level keyboard/mouse events through a virtual `/dev/uinput` device (see `Tools/input_emulation.py`), e.g.:
+`Tools/input/input_test.py` injects OS-level keyboard/mouse events through a virtual `/dev/uinput` device (see `Tools/input/input_emulation.py`), e.g.:
 
 ```bash
-python3 Tools/input_test.py --sequence move:2,look:3
+python3 Tools/input/input_test.py --sequence move:2,look:3
 ```
 
 It drives the focused game window exactly like real hardware, which is how the controls were regression-tested on the packaged build.