docs(content): add Merge Intervals page, quicksort guide, and bump guide badges

apps/docs/content/guides/quicksort.mdx

@@ -0,0 +1,10 @@
+---
+title: "Quicksort"
+list: "https://leetcode.com/problem-list/quicksort/"
+sidebar:
+  badge: '1'
+---
+
+:::note
+This guide has not been written yet. The LeetCode list above has every problem tagged Quicksort.
+:::