feat(content): demo quest 'restore_power'; document quests command

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/src/main/resources/world/quests.yaml

@@ -0,0 +1,10 @@
+- id: restore_power
+  title: "Bring the Manor to Life"
+  autoStart: true
+  stages:
+    - objective: "Get the power running."
+      completion: [{ flag: power_on }]
+    - objective: "Earn the Old Man's brass key."
+      completion: [{ hasItem: key }]
+  onComplete:
+    - { setFlag: manor_secured }