tower in stealth level has no physics and does not occlude guard sight

[wjt]

While testing #2232 I discovered that the tower at the end of res://scenes/quests/lore_quests/quest_001/3_stealth_level/stealth_level.tscn has no physics and does not occlude sight: you can walk through it, and you can't hide from the guard behind it.

Screencast.From.2026-05-29.20-02-28.mp4

I think that's wrong.

XP Summary (total 450)

Subdomain	Skill	XP
Game Design: Core Gameplay & Mechanics	Problem Solving	150
Game Design: Core Gameplay & Mechanics	Creativity & Design Thinking	150
Game Design: Core Gameplay & Mechanics	Technical Literacy	150