docs(docs): restructure guides into numbered groups and add meta files

apps/docs/content/guides/(1-data-structures)/graph.mdx

@@ -0,0 +1,8 @@
+---
+title: "Graph Theory"
+list: "https://leetcode.com/problem-list/graph/"
+---
+
+:::note
+This guide has not been written yet. The LeetCode list above has every problem tagged Graph Theory.
+:::