M1: shared turn logic + characterization tests (39 green)

- npm workspaces: shared/, server/
- shared/turn.js: port turn logic verbatim from App.js (bugs preserved)
- 39 characterization tests lock current behavior
- gitignore: sqlite data, logs

server/package.json

@@ -0,0 +1,24 @@
+{
+  "name": "@ttrpg/server",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Self-hosted backend: Express + ws + better-sqlite3. Server-authoritative turn logic.",
+  "main": "index.js",
+  "scripts": {
+    "dev": "node --watch index.js",
+    "start": "node index.js",
+    "test": "jest"
+  },
+  "dependencies": {
+    "@ttrpg/shared": "*",
+    "better-sqlite3": "^11.3.0",
+    "cors": "^2.8.5",
+    "express": "^4.19.2",
+    "nanoid": "^5.0.7",
+    "ws": "^8.18.0"
+  },
+  "devDependencies": {
+    "jest": "^29.7.0",
+    "supertest": "^7.0.0"
+  }
+}