feat(mystery): migration script and produced markdown content

Adds scripts/migrate-mystery-content.ts which reads rooms, items,
encounters, and endings from TypeScript source and emits byte-identical
markdown files under src/mystery/world/{rooms,items,encounters,endings}/.
Installs tsx as a devDep to support .ts imports across src/ during the
one-shot run.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/world/encounters/rat.md

@@ -0,0 +1,14 @@
+---
+id: rat
+startsIn: "[[cellar-stair]]"
+initialPhase: lurking
+---
+
+## lurking
+A heavy rat watches you from the third step. Its eyes catch the light.
+
+## attack-rat-resolved
+You stamp. The rat squeals and is gone into the dark.
+
+## wait-stays
+The rat does not move. Neither do you.

src/world/endings/bad.md

@@ -0,0 +1,5 @@
+---
+id: bad
+whenFlags: {}
+---
+

src/world/endings/true.md

@@ -0,0 +1,7 @@
+---
+id: true
+whenFlags:
+  ratGone: true
+---
+
+You stand at the top of the stair. The thing below has settled. The door behind you opens, and outside, finally, is morning.

src/world/endings/wrong.md

@@ -0,0 +1,5 @@
+---
+id: wrong
+whenFlags: {}
+---
+

src/world/items/lamp.md

@@ -0,0 +1,10 @@
+---
+id: lamp
+names: ["lamp", "oil lamp", "torch"]
+short: "an oil lamp"
+takeable: true
+initialState:
+  lit: false
+---
+
+An iron oil lamp with a glass chimney. Currently unlit.

src/world/items/letter.md

@@ -0,0 +1,8 @@
+---
+id: letter
+names: ["letter", "folded letter", "paper"]
+short: "a folded letter"
+takeable: true
+---
+
+A folded letter on yellowed paper. The hand is unfamiliar. It reads: "Come at once. The thing in the cellar is waking."

src/world/items/matches.md

@@ -0,0 +1,8 @@
+---
+id: matches
+names: ["matches", "safety matches", "box"]
+short: "a box of safety matches"
+takeable: true
+---
+
+A small cardboard box of safety matches. Half-full.

src/world/rooms/cellar-stair.md

@@ -0,0 +1,21 @@
+---
+id: cellar-stair
+title: "[ Cellar Stair ]"
+exitN: null
+exitS: null
+exitE: null
+exitW: "[[hallway]]"
+exitU: null
+exitD: null
+items: []
+encounter: "[[rat]]"
+---
+
+## first-visit
+The stair drops into wet stone. The hallway is west. Something at the bottom is breathing.
+
+## revisit
+The stair to the cellar.
+
+## examined
+The stairs are stone, slick with damp. You can hear water below, and something else.

src/world/rooms/foyer.md

@@ -0,0 +1,23 @@
+---
+id: foyer
+title: "[ Foyer ]"
+exitN: "[[hallway]]"
+exitS: null
+exitE: null
+exitW: null
+exitU: null
+exitD: null
+items:
+  - "[[letter]]"
+encounter: null
+safe: true
+---
+
+## first-visit
+You stand in the foyer of a house you do not remember entering. The door behind you has closed without sound. A folded letter lies on a small table. A hallway leads north.
+
+## revisit
+The foyer. The door behind you is still closed.
+
+## examined
+A foyer with peeling paper. A small table holds nothing but the letter. The air smells of cold stone. A hallway leads north.

src/world/rooms/hallway.md

@@ -0,0 +1,22 @@
+---
+id: hallway
+title: "[ Hallway ]"
+exitN: null
+exitS: "[[foyer]]"
+exitE: "[[cellar-stair]]"
+exitW: null
+exitU: null
+exitD: null
+items:
+  - "[[lamp]]"
+encounter: null
+---
+
+## first-visit
+A long hallway, lit by nothing. An iron oil lamp sits on a side table. The foyer is south. A stair descends east.
+
+## revisit
+The long hallway.
+
+## examined
+The hallway runs further than the house should be wide. The dust on the floor is undisturbed except where you have walked. The oil lamp is on the side table.