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/141-linked-list-cycle.mdx

@@ -2,13 +2,17 @@
 title: '141. Linked List Cycle'
 description: Given head, the head of a linked list, determine if the linked list has a cycle in it
 icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Floyd's Cycle Finding Algorithm", slug: "floyds-cycle-finding-algorithm" }
+video: "gBTe7lFR3vc"
 sidebar:
   label: 'Linked List Cycle'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ::::warning
 Can you solve it using O(1) (i.e. constant) memory?
 ::::
@@ -69,7 +73,3 @@ class Solution:
                 return True
         return False
 ```
-
-## Explanation
-
-<YouTube id="gBTe7lFR3vc" title="Linked List Cycle - Floyd's Tortoise and Hare - Leetcode 141 - Python" />

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" />

apps/docs/content/(02-nodal-grid)/linked-list/21-merge-two-sorted-lists.mdx

@@ -2,13 +2,15 @@
 title: '21. Merge Two Sorted Lists'
 description: You are given the heads of two sorted linked lists list1 and list2
 icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Recursion", slug: "recursion" }
+video: "XIdigk956u0"
 sidebar:
   label: 'Merge Two Sorted Lists'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ### Example 1:
 - Input: `list1 = [1,2,4], list2 = [1,3,4]`
 - Output: `[1,1,2,3,4,4]`
@@ -82,7 +84,3 @@ class Solution:
         current.next = list1 or list2
         return head
 ```
-
-## Explanation
-
-<YouTube id="XIdigk956u0" title="Merge Two Sorted Lists - Leetcode 21 - Python" />