feat(table-of-contents): implement scrollable TOC with radix-ui

- Add @radix-ui/react-scroll-area dependency
- Create scroll-area component with custom styling
- Refactor TOC layout to use scroll-area component
- Improve TOC styling and active state transitions
- Apply consistent TOC styling across blog and about layouts

package.json

@@ -17,6 +17,7 @@
   },
   "dependencies": {
     "@astrojs/react": "^4.2.1",
+    "@radix-ui/react-scroll-area": "^1.2.9",
     "@radix-ui/react-slot": "^1.1.2",
     "@tailwindcss/vite": "^4.0.14",
     "@types/react": "^19.0.12",