v0.4.0 - ue_x3d_* : the harness on the wire

ue_x3d_* -- the harness on the wire

The v0.3.0 UE<->X3D harness (x3d_bridge) is now MCP tools: Claude can export a
live level to X3D, validate it, apply transform edits back, and preview it --
inside the editor. All four are CORE-tier (mounted by default); Epic's MCP
has no X3D surface.

Added

• ue_x3d_export -- serialize the current level to X3D (each actor's
  quaternion transform, static mesh, material, attach parent; UE Z-up-cm ->
  X3D Y-up-m). mesh_only by default.
• ue_x3d_validate -- the paper boundary as a tool: out-of-grammar nodes,
  dangling USE, wrong arity, non-X3D roots, NaN/inf -- rejected without
  touching the editor.
• ue_x3d_apply -- apply an X3D document's transforms back to the live level
  (validated, guids sanitized, emitted via ue_execute_python). Transforms in
  v0.4.0; spawn/material/reparent apply are follow-ups.
• ue_x3d_preview -- render X3D to a standalone X_ITE browser page.
• 14 async tests + exec-sim coverage for the codegen tools (stub extended with
  Quat/Transform/get_actor_transform). Tier table pinned at 60 tools / 22 CORE.

Notes

• Editor-independent and CI-green. The live round-trip against a real 5.8
  scene is gated on ue_preflight reading green (bAllowAnyRemoteFunctionCall
  applied). B stays analytic (not glTF-calibrated) -- round trip is
  basis-agnostic, so fidelity-only.