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

apps/docs/content/(04-relational)/graph-bfs/127-word-ladder.mdx

@@ -2,13 +2,16 @@
 title: '127. Word Ladder'
 description: 'A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:'
 icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Breadth-First Search", slug: "breadth-first-search" }
+  - { name: "Bidirectional Search", slug: "bidirectional-search" }
 sidebar:
   label: 'Word Ladder'
   badge: 'Hard'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]`
 - Output: `5`