v0.2.3-alpha

Fix: portal config menu could not be reopened after converting the frame material.

The config menu opened only via the base frame node's right-click handler, which material conversion removed; the invisible fallback anchor entity was never selectable (engine returns no selection box for invisible entities). The anchor is now invisible-but-clickable, persists across map reload, and converted frames keep their material on restart.

Lua-only change; engine binary identical to v0.2.2-alpha.