feat(vehicle): split into systems, add real LODs, import to Unreal

Follows the vehicle-artist object split, which the first build violated: body, glass,
front and rear lights, mirrors and a single wheel mesh are now separate objects and
separate assets in /Game/Hollywood/Vehicle. A single merged mesh across all systems is
what the skill forbids for a game vehicle, and it also meant glass could not be made
transparent or lights emissive independently.

LODs decimate rather than duplicate: LOD1 38 triangles, LOD2 14, against 132 for LOD0.
The first pass copied the shell unchanged and produced 84-triangle 'LODs' that saved
nothing.

Imports verified with bounds: body 4.76 x 1.76 x 1.28 m, wheel 0.22 x 0.66 x 0.66 m,
which match the modelled dimensions.

Open, recorded: LOD group wiring needs StaticMeshEditorSubsystem.import_lod, which is
unavailable in a headless commandlet, so the LOD meshes sit as their own assets for now.

Tools/README.md

@@ -95,6 +95,7 @@ Geographic tools live in [`Geo/tools/`](../Geo/README.md) and the Blender-side b
 | `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` |
+| `ue_vehicle_import.py` | Imports the sedan's six systems into `/Game/Hollywood/Vehicle` as separate static meshes, plus the two LOD meshes; the body carries the `UCX_` hulls as simple collision. | (no arguments; reads `/tmp/gigline/vehicle`) | `UnrealEditor-Cmd <uproject> -run=pythonscript -script=Tools/ue_vehicle_import.py -nullrhi -unattended -nopause` |
 
 ## Tests