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/npcs.yaml

@@ -0,0 +1,12 @@
+- id: old_man
+  name: Old Man
+  description: A stooped old man with a grey beard.
+  greeting: |
+    "Hello, traveller. If you bring me the oil lamp,
+    I will give you the key to the cellar."
+  reactions:
+    - onReceive: lamp
+      response: |
+        "Thank you! Here, take this key."
+      gives: key
+      consumes: lamp