feat(engine): scaffold runtime skeleton

Data/Engine/services/WebUI/__init__.py

@@ -0,0 +1,17 @@
+"""WebUI service stubs for the Borealis Engine runtime.
+
+The future WebUI migration will centralise static asset serving, template
+rendering, and dev-server proxying here. Stage 1 keeps the placeholder so the
+application factory can stub out registration calls.
+"""
+from __future__ import annotations
+
+from flask import Flask
+
+from ...server import EngineContext
+
+
+def register_web_ui(app: Flask, context: EngineContext) -> None:
+    """Placeholder hook for WebUI route registration."""
+
+    context.logger.debug("Engine WebUI services are not yet implemented.")