docs(docs): add study decks, new reference pages, and fix header image path

docs/solutions/(two-pointers)/01-reverse-string.mdx

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-title: '344. Reverse String'
-sidebar:
-  badge: 'Easy'
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-
-<Badge variant="accent">Two Pointers</Badge>
-<Badge>[Source](https://leetcode.com/problems/reverse-string/)</Badge>
-
-## Description

docs/solutions/(two-pointers)/02-squares-of-a-sorted-array.mdx

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-sidebar:
-  icon: code
-  badge: '977'
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