Spawn Selector

Fixed

• Fixed players getting stuck in the holding/recovery flow after skipping structure selection in vanilla Superflat Water World. When the land-spawn search has no candidates, vanilla entry now falls back to the shared world spawn instead of failing.
• The fallback checks the player's actual bounding box and moves upward within the existing height bound when needed to avoid collision. Water is allowed in this vanilla fallback; the structure-spawn safety rules remain unchanged.