phase(N.4): SHIP — flag default-on + finalize plan + roadmap

Phase N.4 (Rendering Pipeline Foundation) ships. WbFoundationFlag
flips to default-on (== "1" → != "0"). WB's ObjectMeshManager is
now acdream's production mesh pipeline; WbDrawDispatcher is the
production draw path. Legacy InstancedMeshRenderer is retained as
ACDREAM_USE_WB_FOUNDATION=0 escape hatch until N.6 retires it.

Visual verification at Holtburg passed:
- Scenery (trees / rocks / fences / buildings) renders correctly
- Characters connected with full close-detail geometry (Issue #47
  preserved — GfxObjDegradeResolver path intact)
- FPS substantially improved by grouped instanced draws + per-entity
  AABB cull + opaque front-to-back sort + palette-hash memoization

Three high-value WB API gotchas surfaced during Task 26 visual
verification and are now documented in CLAUDE.md "WB integration
cribs" + plan Adjustments 7-9 + memory project_phase_n4_state.md:

1. ObjectMeshManager.IncrementRefCount only bumps a counter — does
   NOT trigger mesh loading. Call PrepareMeshDataAsync explicitly.
2. ObjectRenderBatch.SurfaceId is unset — read batch.Key.SurfaceId.
3. Modern rendering (GL 4.3 + bindless = every modern GPU) packs
   every mesh into ONE global VAO/VBO/IBO. Use
   glDrawElementsInstancedBaseVertex(BaseInstance) with FirstIndex +
   BaseVertex from the batch, not naive DrawElementsInstanced.

Plan doc flipped to Final state. Roadmap N.4 → Live ✓; N.5 rebranded
from "Terrain rendering" to "Modern rendering path" (bindless +
multi-draw indirect on top of N.4's foundation; terrain rendering
moves to N.5b). CLAUDE.md "Currently in flight" pointer updated to
N.5. New memory file project_phase_n4_state.md preserves the three
WB gotchas for cross-session continuity.

n4-verify*.log added to .gitignore.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -29,6 +29,7 @@ references/*
 launch.log
 launch-*.log
 launch.utf8.log
+n4-verify*.log
 
 # ImGui auto-saved window/docking state (per-user, not source)
 imgui.ini