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.

AGENTS.md

@@ -126,7 +126,7 @@ Rules that keep tools reusable and reviewable:
 - **Result files for Unreal.** Unreal commandlets swallow `print()`; write the outcome to `/tmp/gigline/<tool>.txt` and read that instead of trusting the exit code alone.
 - **Absolute paths into sandboxes.** Blender Flatpak (`LD_LIBRARY_PATH="$B/blender/lib"`) and Unreal do not share the repo's working directory; pass absolute paths.
 - **Clean worktree for generators.** Tools that rewrite committed assets (site/street/hero builders, importers, map builders) run from a clean worktree; inspect the LFS diff before committing. Note that `.blend` and `.umap` check out read-only — `chmod u+w` first or the save silently fails.
-- **Network and paid-API tools are human-triggered.** `Tools/commons_fetch.py`, `Tools/page_image_fetch.py`, `Tools/judge_screenshot.py` (OpenRouter) and anything similar never sit in a gate or CI. Handle HTTP 429 with back-off rather than retrying immediately.
+- **Network and paid-API tools are human-triggered.** `Tools/gen/commons_fetch.py`, `Tools/gen/page_image_fetch.py`, `Tools/review/judge_screenshot.py` (OpenRouter) and anything similar never sit in a gate or CI. Handle HTTP 429 with back-off rather than retrying immediately.
 - **Measure, don't assert.** Verification tools print the sampled numbers — counts, holes, Z ranges, worst step and its location, frame-time percentiles — so a claim in `TODO.md`, `CHANGELOG.md` or `Docs/` can be re-checked by re-running the command.
 
 **Document every tool.** A new or changed tool gets a row in the inventory table of the README beside it: [`Tools/README.md`](Tools/README.md), [`Geo/README.md`](Geo/README.md), or [`Art/blender/README.md`](Art/blender/README.md). What it does, its arguments, and a typical command. A tool without a README row is unfinished.
@@ -212,10 +212,10 @@ Do not copy the common packs into the repository: a second copy under a differen
 
 Any change that affects the game's appearance — meshes, materials, lighting, levels, character, camera, post-processing — must be rendered for human review:
 
-1. Run `Tools/render_screenshots.sh` (rebuilds `Game/GigLine/Content/Test/ReviewMap.umap` from current content, runs the game on it, captures the fixed camera list, copies the PNGs into `Screenshots/`).
-2. Optional pre-check with a vision model: `Tools/judge_screenshot.py --image <shot.png> --expect "<what it should show>"` (or `--shots` to run every shot in the README) flags likely-missing content before a human looks. It reads `OPENROUTER_API_KEY` from `.env` (ignored). Small helper only — it never replaces the human verdict.
+1. Run `Tools/review/render_screenshots.sh` (rebuilds `Game/GigLine/Content/Test/ReviewMap.umap` from current content, runs the game on it, captures the fixed camera list, copies the PNGs into `Screenshots/`).
+2. Optional pre-check with a vision model: `Tools/review/judge_screenshot.py --image <shot.png> --expect "<what it should show>"` (or `--shots` to run every shot in the README) flags likely-missing content before a human looks. It reads `OPENROUTER_API_KEY` from `.env` (ignored). Small helper only — it never replaces the human verdict.
 3. Update `Screenshots/README.md` **in the same change as any visual work** — every change that affects appearance, not only new shots: the image is **embedded inline** (`![alt](demo/<shot>.png)`) with its view, expected content, verification and approval state, plus one row in the status table at the top. The review happens in the file; a path alone is not a review, and a shot whose README section is stale is a defect.
 4. The PNGs **are committed** so reviewers see exactly what the build rendered (`.gitignore` does not exclude them). Keep them in sync with this README: drop retired shots in the same change.
 5. Wait for the user's approval before treating a visual change as done; record approval by ticking both the shot's section and its row in the status table in `Screenshots/README.md`.
 
-New content that needs a different camera angle gets a new entry in the shot list in `Tools/ue_build_review_map.py`.
+New content that needs a different camera angle gets a new entry in the shot list in `Tools/unreal/ue_build_review_map.py`.