feat: add spellcheck

package.json

@@ -7,6 +7,7 @@
     "build": "next build",
     "start": "next start -p 3003",
     "lint": "eslint src --max-warnings 0",
+    "spellcheck": "cspell ./posts/**/*.md",
     "test": "echo \"No tests yet!\" && exit 0"
   },
   "dependencies": {
@@ -26,6 +27,7 @@
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "cspell": "9.4.0",
     "eslint": "^9",
     "eslint-config-next": "15.1.6",
     "postcss": "^8",