feat: Three.js 3D asset overlay with QuadTree LOD and Mapbox camera sync

[real-venus]

Three.js 3D Utility Asset Overlay with QuadTree LOD and Mapbox Camera Sync (#54)

Closes #54

What's included

File	Responsibility
src/types/spatial.ts	Coordinate3D/AABB/BoundingSphere/FrustumPlane/LODLevel/AssetInstance and invariants: LOD 100/300/500 m, 100 km region, depth 8, 20k cap → 10k batch cull, 512 MB GPU budget.
src/utils/frustum.ts	Gribb–Hartmann plane extraction from a column-major VP matrix + conservative sphere/point tests. Three-free → runs in a Worker and is unit-tested.
src/utils/cameraMatrix.ts	perspective/lookAt/multiply + web-mercator meters; builds the view-projection without a WebGL context.
src/components/map/lod/QuadTree.ts	Capacity-subdividing quadtree with aggregated bounding spheres; queryFrustum returns visible assets tagged by LOD, with nearest-N batch culling past the cap; getLODLevel.
src/workers/frustumCull.worker.ts	Owns the tree and runs the per-frame cull off the render thread (matrix in → visible ids + LOD out).
src/hooks/useMapCameraSync.ts	Reads map.transform (center/elevation/bearing/pitch) each rAF, maps the mercator center to world meters, emits camera state + VP matrix. Injectable map/rAF.
src/components/map/lod/AssetMesh.ts	THREE.LOD factory (detail → box → impostor sprite, empty past 500 m) + InstancedMesh to collapse draw calls. GLTF is injectable (no examples-subpath coupling).
src/components/map/ThreeOverlay.tsx	alpha:true renderer on a pointer-events:none canvas over the map container; worker culling, camera sync, and a GPU-memory watchdog that degrades the LOD0 distance to 50 m over budget.
src/components/map/shaders/assetInstancing.vert	Per-instance position/yaw/scale vertex shader.
tests/unit/*, tests/hooks/*	Frustum math (NDC-cube extraction, sphere/point), camera matrices (frustum round-trip, mercator), QuadTree (subdivision, LOD bucketing, frustum exclusion, batch cull, clear), and camera-sync (rAF loop + pure helpers).