semesterprojekt: implement full text adventure (phases 1-7)

Walking skeleton through Swing GUI: YAML-driven world (4 rooms,
4 items, 1 NPC), HashMap command dispatch with parser, three-tier
item hierarchy (readable / switchable / plain), and end-to-end
NPC give/receive flow. 67 tests green.

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

@@ -0,0 +1,24 @@
+- type: readable
+  id: letter
+  name: Letter
+  description: A crumpled piece of paper.
+  readText: |
+    "Meet me at midnight in the cellar. - A."
+
+- type: switchable
+  id: lamp
+  name: Oil Lamp
+  description: An old oil lamp, heavy with fuel.
+  initialState: false
+  onText: The lamp flares to life, casting a warm glow.
+  offText: You snuff out the lamp.
+
+- type: plain
+  id: shovel
+  name: Shovel
+  description: A rusty shovel. Sturdy enough to dig.
+
+- type: plain
+  id: key
+  name: Brass Key
+  description: A small brass key, polished from use.