docs(docs): restructure documentation hierarchy and rename files

docs/content/01-coding/01-arrays-and-strings/02-two-pointers.mdx

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+---
+title: 'Two Pointers'
+description: 'Converging/parallel index walk that prunes the O(n^2) pair space using order.'
+sidebar:
+  icon: sticky-note
+---
+
+:::warning[Under construction]
+This page is a scaffold. Notes, canonical problems, and template code are not written yet.
+:::