docs(docs): add ProblemBadges component, layout slot, and enrich pages with topics/video frontmatter, plus guide placeholders and topic‑landing map.

apps/docs/content/(02-nodal-grid)/linked-list/206-reverse-linked-list.mdx

@@ -2,13 +2,15 @@
 title: '206. Reverse Linked List'
 description: Given the head of a singly linked list, reverse the list, and return the reversed list
 icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Recursion", slug: "recursion" }
+video: "G0_I-ZF0S38"
 sidebar:
   label: 'Reverse Linked List'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ::::warning
 A linked list can be reversed either iteratively or recursively. Could you implement both?
 ::::
@@ -62,7 +64,3 @@ class Solution:
             curr = next_
         return prev
 ```
-
-## Explanation
-
-<YouTube id="G0_I-ZF0S38" title="Reverse Linked List - Iterative AND Recursive - Leetcode 206 - Python" />