docs(content): add issue URLs to problem pages and restructure guides into appendix

apps/docs/content/(04-relational)/topological-sort/207-course-schedule.mdx

@@ -8,6 +8,7 @@ topics:
   - { name: "Graph Theory", slug: "graph" }
   - { name: "Topological Sort", slug: "topological-sort" }
   - { name: "Directed Acyclic Graph", slug: "directed-acyclic-graph" }
+issue: "https://github.com/prdlk/leetcode/issues/142"
 sidebar:
   label: 'Course Schedule'
   badge: 'Medium'

apps/docs/content/(04-relational)/topological-sort/210-course-schedule-ii.mdx

@@ -7,6 +7,7 @@ topics:
   - { name: "Breadth-First Search", slug: "breadth-first-search" }
   - { name: "Graph Theory", slug: "graph" }
   - { name: "Topological Sort", slug: "topological-sort" }
+issue: "https://github.com/prdlk/leetcode/issues/143"
 sidebar:
   label: 'Course Schedule II'
   badge: 'Medium'