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

apps/docs/content/(03-hierarchical)/trie/208-implement-trie-prefix-tree.mdx

@@ -8,6 +8,7 @@ topics:
   - { name: "Design", slug: "design" }
   - { name: "Trie", slug: "trie" }
 video: "oobqoCJlHA0"
+issue: "https://github.com/prdlk/leetcode/issues/127"
 sidebar:
   label: 'Implement Trie (Prefix Tree)'
   badge: 'Medium'

apps/docs/content/(03-hierarchical)/trie/211-design-add-and-search-words-data-structure.mdx

@@ -8,6 +8,7 @@ topics:
   - { name: "Design", slug: "design" }
   - { name: "Trie", slug: "trie" }
 video: "BTf05gs_8iU"
+issue: "https://github.com/prdlk/leetcode/issues/128"
 sidebar:
   label: 'Design Add and Search Words Data Structure'
   badge: 'Medium'