feat(mystery): add opening and main-floor content

src/world/rooms/music-room.md

@@ -0,0 +1,25 @@
+---
+id: music-room
+title: "[ Music Room ]"
+exitN: "[[servants-passage]]"
+exitS: null
+exitE: null
+exitW: null
+exitU: "[[hallway]]"
+exitD: null
+items:
+  - "[[music-box-key]]"
+encounter: "[[piano-echo]]"
+safe: true
+---
+
+## first-visit
+A piano stands open with one key held silently down. The strings inside are furred with dust.
+
+Something answers from elsewhere in the house, too soft to be music. A servants' passage opens north. The hallway is above.
+
+## revisit
+The music room waits on the same note.
+
+## examined
+The depressed piano key does not rise when touched. A tiny key rests on the music stand where sheet music should be.