The new terrain dispatcher. Single global VBO/EBO with a slot
allocator (one slot per landblock, 384 verts × 40 bytes per slot).
Per-frame: build DEIC array from visible slots, upload, dispatch
via glMultiDrawElementsIndirect. Atlas textures bound via bindless
handles set per-frame as sampler uniforms.
Total ~6-8 GL calls per frame for terrain regardless of visible
landblock count (vs today's per-LB binds at radius=2 → ~25 calls,
radius=5 → ~121 calls).
API mirrors TerrainChunkRenderer so GameWindow integration in T8 is
a drop-in field+ctor swap.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
