refactor(M03): extract WMO render build planner

RENDER.md

@@ -29,6 +29,7 @@ Paired run 2026-07-11 подтвердил крупный coordinate/placement g
 - `src/scenes/streaming/streaming_world_loader.gd` - внутренний runtime streamer мира.
 - `src/render/wmo/wmo_placement_resolver.gd` - value-only WMO path, identity and transform rules.
 - `src/render/wmo/wmo_placement_registry.gd` - WMO placement-key to tile/global reference sets; Nodes and render jobs remain in the streamer.
+- `src/render/wmo/wmo_render_build_step_planner.gd` - mesh-first lightweight WMO group operation and cursor planning without Nodes or Resources.
 - `src/scenes/streaming/eastern_kingdoms_streaming.tscn` - текущая сцена для проверки Azeroth/Eastern Kingdoms.
 - `addons/mpq_extractor/loaders/adt_builder.gd` - сборка ADT terrain, control splat материалов и MH2O liquids.
 - `addons/mpq_extractor/loaders/m2_builder.gd` - сборка статического M2 mesh/material.
@@ -398,6 +399,8 @@ Known limits:
 - WMO на границе ADT не дублируются;
 - `WmoPlacementRegistry` owns only placement reference sets; the streamer keeps
   the parallel key-to-Node map and performs final-release cancellation/free;
+- `WmoRenderBuildStepPlanner` selects one mesh or MultiMesh group and its next
+  cursors; the streamer still materializes Nodes and consumes the frame permit;
 - большие WMO не должны инстанцироваться как тяжелые `.tscn` во время движения;
 - добавлен lightweight render-cache path для WMO groups;
 - `wmo_render_group_ops_per_tick` ограничивает подключение WMO groups по кадрам;