geo: one tool directory, one unit boundary, per-asset provenance

Geo/tools/ is now every geographic script, with Geo/README.md documenting each
one; the Blender-side builders moved beside their outputs in Art/blender/*/ and
import their helpers from Geo/tools/osm_common.py.

That module gains to_unreal_local() and to_blender_local(): the only place in the
repository that multiplies metres by 100, so a second silent scale cannot be
introduced. block_height_report.py adds height provenance for the block — 3 of
15 buildings have no height data and render at a placeholder 6.4 m.
asset_metadata.py writes and audits <asset>.geo.json sidecars; four now exist
(hero-facade, terrain, street, blockout) and the audit recomputes each centre from
the origin, failing anything that disagrees.

Tools/README.md

@@ -14,10 +14,9 @@ Repeatable import/export and processing helpers. Anything that was done twice by
 
 - `render_screenshots.sh` — visual-review pipeline: rebuilds `/Game/Test/ReviewMap` from current content (`ue_build_review_map.py`), runs the game on it in `-game` mode, lets `AGigLineShotActor` (`Game/GigLine/Source/GigLine/`) capture the fixed camera list, and copies the PNGs into the gitignored `Screenshots/`. See `Screenshots/README.md`.
 - `check-lfs.sh` — repository guard: fails if `git-lfs` or the `lfs` filter is missing, or if an LFS-tracked file was committed as a plain blob.
-- `site_assembly.py` — assembles terrain + street + blockout into one file and raycasts the walking routes for holes and steps.
-- `street_mesh.py` — road, kerbs, and sidewalks on the DEM, in the project frame; kerbs flush at the three crossings.
-- `terrain_from_dem.py` — terrain grid from the committed DEM, with building footprints cut out.
-- `blosm_blockout.py` — headless Blosm import of the committed `.osm` extract into a `.blend`, with a per-building scale report. Exact invocation in `Art/blender/README.md`.
+- Geographic tools and their shared helpers live in `Geo/tools/` (see `Geo/README.md`).
+- Blender-side builders that turn geo data into meshes live beside their output: `Art/blender/terrain/terrain_from_dem.py`, `Art/blender/street/street_mesh.py`, `Art/blender/site/site_assembly.py`, `Art/blender/blockout/blosm_blockout.py`. They import their helpers from `Geo/tools/osm_common.py`, which is also the only place that converts metres to Unreal centimetres.
+- `sibling_asset_audit.py` — reads the sibling project's prop library straight from GLB headers and writes `Art/props/reuse-manifest.json`; copies nothing.
 - `page_image_fetch.py` — resolves a web page's `og:image` and downloads it, with page URL and hash in a local sidecar. Works for Flickr, Commons file pages, and most photo blogs.
 - `commons_fetch.py` — Wikimedia Commons reference fetcher. Search, exact `File:` titles, or a whole Commons category (`--category`), thumbnails, provenance `sidecar.json` per folder. Wikimedia throttles `upload.wikimedia.org` (HTTP 429), so keep batches to six or fewer files and pass `--delay 3`; a throttled file is skipped and recorded rather than aborting the run. Writes only into the gitignored `Art/reference/`; reference images are never committed.