WIP Crystal Sanctuary sheltered area and boss arena
- Add CrystalSanctuary node type and register it in gameplay.json.
- Treat CrystalSanctuary like RespawnArea for sheltered state and weapon restriction.
- Register CrystalSanctuaryDoor in scene registry and open all doors on guardian death.
- Split CrystalSanctuary into FinalBossArena and CrystalSanctuary mesh.
- Use SM_Wall_2x6_NoColl for a non-colliding wall segment.
- Make no-weapons UI indicator opaque.
- Apply semi-transparent tint to no-weapons UI indicator.
- Extend player shelter raycast range to 350 units.