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)/monotonic-stack/853-car-fleet.mdx

@@ -2,13 +2,17 @@
 title: '853. Car Fleet'
 description: There are n cars at given miles away from the starting mile 0, traveling to reach the mile target
 icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Stack", slug: "stack" }
+  - { name: "Sorting", slug: "sorting" }
+  - { name: "Monotonic Stack", slug: "monotonic-stack" }
+video: "Pr6T-3yB9RM"
 sidebar:
   label: 'Car Fleet'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Array</Badge>
-
 ### Example 1:
 - Input: `target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3]`
 - Output: `3`
@@ -62,7 +66,3 @@ class Solution:
 
         return len(stack)
 ```
-
-## Explanation
-
-<YouTube id="Pr6T-3yB9RM" title="Car Fleet - Leetcode 853 - Python" />