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)/hybrid-structures/2-add-two-numbers.mdx

@@ -2,13 +2,16 @@
 title: '2. Add Two Numbers'
 description: You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list
 icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Math", slug: "math" }
+  - { name: "Recursion", slug: "recursion" }
+video: "wgFPrzTjm7s"
 sidebar:
   label: 'Add Two Numbers'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ### Example 1:
 - Input: `l1 = [2,4,3], l2 = [5,6,4]`
 - Output: `[7,0,8]`
@@ -70,7 +73,3 @@ class Solution:
 
         return dummy.next
 ```
-
-## Explanation
-
-<YouTube id="wgFPrzTjm7s" title="Add Two Numbers - Leetcode 2 - Python" />