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

apps/docs/content/(01-linear-structures)/hash-table/1-two-sum.mdx

@@ -2,13 +2,15 @@
 title: '1. Two Sum'
 description: You are given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target
 icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+video: "KLlXCFG5TnA"
 sidebar:
   label: 'Two Sum'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Array</Badge>
-
 ::::warning
 Can you come up with an algorithm that is less than O(n^2) time complexity?
 ::::
@@ -60,7 +62,3 @@ class Solution:
             seen[num] = i
         return []
 ```
-
-## Explanation
-
-<YouTube id="KLlXCFG5TnA" title="Two Sum - Leetcode 1 - HashMap - Python" />