feat(world): Haunted Manor content expansion (14 rooms, one world)

Replace the 5-room demo with a condensed 14-room manor on one spine
(restore power -> escape) that stacks all five mechanics, plus an optional
spirit thread feeding 3 prioritized endings (no hard-fail). Pure YAML on the
existing engines: 14 rooms across 3 levels, ~16 items, 5 combinations, the
old_man hint NPC, restore_power + lay_to_rest quests, and 3 endings.

Consolidate to one world: remove the toy "Test Manor" test fixture so the
loader tests exercise the real shipped world. Adapt WorldLoaderTest and
TutorialLoaderTest to form-invariants of the real world, and add
WorldSolvableTest, which walks the critical path (light/lock gating +
Combinations.tryUse + flags) to guarantee power_on, ghost_banished, and a
victory ending are reachable — an unsolvable world now fails the build.

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

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

@@ -1,17 +1,29 @@
 - id: old_man
-  name: Old Man
-  description: A stooped old man with a grey beard.
+  name: Old Caretaker
+  description: A stooped old man with a grey beard, watching from among the shelves.
   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
+    "Another lost soul in this house. Get the power running and tend to what
+    waits upstairs — that is the only way out that's worth taking."
+  # First matching line wins; otherwise the greeting is used.
   dialogue:
-    - when: [{ flag: power_on }]
+    - when: [{ flag: ghost_banished }]
       text: |
-        "You got the power running! The whole house feels less...
-        watchful now."
+        "You laid the poor thing to rest. Bless you. Go now — the night is
+        clear and the house will hold its peace."
+    - when: [{ flag: power_on }, { notFlag: ghost_banished }]
+      text: |
+        "The lights are back — feel how the house has quieted? Climb the stair.
+        In the chapel there's a shrine: give it the locket, then the photograph,
+        in that order."
+    - when: [{ notFlag: cellar_drained }]
+      text: |
+        "Cold down there, isn't it? The cellar's flooded over the fuse. Find the
+        valve wheel — the conservatory, I think — and drain it."
+  reactions:
+    - onReceive: letter
+      response: |
+        "Ah... that letter. I wrote it, long ago, for whoever came after. So
+        someone finally read it. Keep going — you're closer than they ever got."
+      consumes: letter
+      effects:
+        - { setFlag: heard_tale }