feat(mesh): add tile mesh generation package

Add @tts/mesh, a package for generating extruded tile meshes from 2D
shapes. It provides shape generators (rect, hex, circle, rounded rect,
frame), earcut-based tessellation of top/bottom faces with UVs, and
outward-normal wall generation, combined into raw BufferGeometry-ready
typed arrays.

packages/mesh/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "@tts/mesh",
+  "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": {
+    "earcut": "^3.2.3",
+    "three": "^0.185.1"
+  },
+  "devDependencies": {
+    "@types/earcut": "^3.0.0",
+    "@types/three": "^0.185.4",
+    "typescript": "^5.7.2"
+  }
+}