Fix city stuttering with incremental tile finalization and GPU optimizations

Replace monolithic finalizeTile() with a phased state machine that spreads
GPU upload work across multiple frames (TERRAIN→M2→WMO→WATER→AMBIENT→DONE).
Each advanceFinalization() call does one bounded unit of work within the
per-frame time budget, eliminating 50-300ms frame hitches when entering cities.

Additional performance improvements:
- Pre-allocate bone SSBOs at M2 instance creation instead of lazily during
  first render frame, preventing hitches when many skinned characters appear
- Enable WMO distance culling (800 units) with active-group exemption so
  the player's current floor/neighbors are never culled
- Add 4-tier adaptive M2 render distance (250/400/600/1000 based on count)
- Remove dead PendingM2Upload queue code superseded by incremental system

Fix tile re-enqueueing bug: keep tiles in pendingTiles until committed to
loadedTiles (not when moved to finalizingTiles_) so streamTiles() doesn't
re-enqueue tiles mid-finalization. Also handle unloadTile() for tiles in
the finalizingTiles_ deque to prevent orphaned water/M2/WMO resources.

include/rendering/m2_renderer.hpp

@@ -478,6 +478,7 @@ private:
     // Helper to allocate descriptor sets
     VkDescriptorSet allocateMaterialSet();
     VkDescriptorSet allocateBoneSet();
+    void preallocateBoneBuffers(M2Instance& instance);
 
     // Helper to destroy model GPU resources
     void destroyModelGPU(M2ModelGPU& model);