feat(vehicle): model the sedan with collision hulls

First 0.3.0 asset. Tools/vehicle_build.py builds a 4.72 x 1.80 x 1.44 m sedan - 2.78 m
wheelbase, 1.62 m track, 0.33 m wheels - as a three-tier silhouette: sill slab, bonnet
and boot shoulders, cabin greenhouse, plus glazing, lamps, bumpers and mirrors. 252
triangles.

Collision is four UCX_-prefixed convex hulls (body, cabin, two bumpers) per the
collision-proxy convention, hidden from render so the preview reads as the car rather
than the colliders.

Two corrections from the preview, both visible in the saved image: the first build was
one tall slab plus a floating cabin and read as a box truck, and the wheels were buried
inside a full-width sill - the sill is now 1.56 m so the wheels stand proud.

Reports every dimension to JSON so the Chaos vehicle config can read the wheelbase, track
and radius instead of restating them.

Tools/README.md

@@ -94,6 +94,7 @@ Geographic tools live in [`Geo/tools/`](../Geo/README.md) and the Blender-side b
 | `comfyui_character_blueprint.py` | Generates a character blueprint sheet - front, side, back and head views plus a contact sheet - from one description, with fixed seeds and a JSON record. | `--desc`, `--out`, `--model`, `--size` | `python3 Tools/comfyui_character_blueprint.py --desc "lean pedestrian, navy tee, jeans" --out Art/characters/blueprints` |
 | `character_match.py` | Compares a rendered character against a blueprint: figure aspect, fill and coverage deltas, mean CIE76 colour distance, dominant-palette distance, and a side-by-side montage. | `--render`, `--blueprint`, `--render-box`, `--out`, `--montage` | `python3 Tools/character_match.py --render Screenshots/demo/review-demo-third-person-front.png --blueprint Art/characters/blueprints/front.png --render-box 0.42,0.46,0.56,0.97 --montage /tmp/gigline/match.png` |
 | `generate_character_textures.py` | Procedural skin-pore and hair-strand textures with sidecars; no model involved. | `--out` | `python3 Tools/generate_character_textures.py --out Art/textures/generated` |
+| `vehicle_build.py` | Models the drivable sedan: three-tier body, four wheels, lamps and bumpers, plus four `UCX_` convex collision hulls; saves the .blend, exports an FBX with the `ue_metric_v1` preset, and writes a report with every dimension the vehicle config needs. | `--out`, `--fbx`, `--report` | `blender -b --factory-startup --python Tools/vehicle_build.py -- --out Art/blender/vehicle/gigline-sedan.blend --fbx /tmp/gigline/vehicle/sedan.fbx` |
 
 ## Tests