feat(bgm): add board game manifest loader

Parse yaml/json/toml and markdown code blocks into packages, expanding
$variants via typed-csv and collecting parts, surfaces, and setups by
include patterns. Ships zod validation, a vitest config, and 16 tests.

packages/bgm/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "@tts/bgm",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc -p tsconfig.json",
+    "typecheck": "tsc -p tsconfig.json --noEmit",
+    "test": "vitest run",
+    "lint": "echo \"no lint configured\""
+  },
+  "dependencies": {
+    "marked": "^16.0.0",
+    "picomatch": "^4.0.5",
+    "smol-toml": "^1.4.0",
+    "typed-csv": "^2.0.0",
+    "yaml": "^2.4.2",
+    "zod": "^3.24.1"
+  },
+  "devDependencies": {
+    "@types/node": "^22.12.0",
+    "@types/picomatch": "^4.0.0",
+    "typescript": "^5.7.2",
+    "vitest": "^4.1.10"
+  }
+}