Update dependencies in package.json and package-lock.json; remove test posts and update welcome post with new content and formatting details.

package.json

@@ -21,8 +21,12 @@
     "postcss": "^8.4.35",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
+    "rehype-raw": "^6.1.1",
+    "rehype-stringify": "^9.0.3",
     "remark": "^15.0.1",
+    "remark-gfm": "^3.0.1",
     "remark-html": "^16.0.1",
+    "remark-rehype": "^11.1.0",
     "tailwindcss": "^3.4.1"
   },
   "devDependencies": {