Add Hebat Allah wreck to the sunlit shallows site

First wreck in the production world layer. A WreckActor (StaticBody3D)
instantiates a two-LOD glTF visual, builds a trimesh collision from a
separate lighter glTF, and carries the sonar metadata (metal, 0.9
reflectivity) so the bathymetry rays echo it. The sunlit shallows site
places the MV Hebat Allah 62 m ahead of the submarine on the floor.

The assets derive from a CC BY 4.0 photogrammetry scan by Holger Buss
(Sketchfab). The raw 274 MB scan stays outside the repo; the committed
GLBs come from a reproducible Blender pipeline under scripts/assets/:
skirt cut, 44 m rescale, merge by distance (the scan is a triangle soup),
fragment removal, 0.4 m voxel remesh, decimation to 58k/14.5k/2.9k
triangles, smart UVs and a 2K albedo rebaked from a luminance-rebuilt
texture (the scan's red channel is dead).

docs/ASSET_LICENSES.md starts the licence registry required by the design
plan and records the attribution owed in the credits. The site suite
gains twelve assertions covering sonar metadata, collision, LOD handover
and triangle budgets. Godot extracts the embedded albedo next to the glb
on import; those PNGs are ignored like the cockpit ones.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.gitignore

@@ -6,3 +6,4 @@ builds/
 
 # Textures que Godot extrait des .glb a l import : regenerees, non versionnees
 game/presentation/cockpit/assets/models/*.png
+game/world/wrecks/assets/**/*.png