fix: add missing blog dependencies to package.json

Add gray-matter, remark, remark-gfm, and remark-html dependencies
that were missing from the blog feature commits, causing webpack
"Module not found" errors in CI/CD.

These packages are required by src/lib/blog.ts for markdown processing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/package.json

@@ -62,6 +62,7 @@
     "embla-carousel-autoplay": "^8.6.0",
     "embla-carousel-react": "^8.6.0",
     "emojibase-data": "^16.0.3",
+    "gray-matter": "^4.0.3",
     "jose": "^6.1.0",
     "js-yaml": "^4.1.0",
     "lib0": "^0.2.114",
@@ -79,6 +80,12 @@
     "react-resizable-layout": "^0.7.3",
     "react-resizable-panels": "^3.0.6",
     "react-textfit": "^1.1.1",
+    "rehype-autolink-headings": "^7.1.0",
+    "rehype-highlight": "^7.0.2",
+    "rehype-slug": "^6.0.0",
+    "remark": "^15.0.1",
+    "remark-gfm": "^4.0.1",
+    "remark-html": "^16.0.1",
     "socket.io": "^4.8.1",
     "socket.io-client": "^4.8.1",
     "three": "^0.169.0",