docs: replace legacy line‑dot‑left‑horizontal icons with unified dot icon across docs

apps/docs/content/(02-nodal-grid)/matrix-index-math/48-rotate-image.mdx

@@ -1,7 +1,7 @@
 ---
 title: '48. Rotate Image'
 description: You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise)
-icon: line-dot-left-horizontal
+icon: dot
 sidebar:
   label: 'Rotate Image'
   badge: 'Medium'

apps/docs/content/(02-nodal-grid)/matrix-index-math/54-spiral-matrix.mdx

@@ -1,7 +1,7 @@
 ---
 title: '54. Spiral Matrix'
 description: Given an m x n matrix, return all elements of the matrix in spiral order
-icon: line-dot-left-horizontal
+icon: dot
 sidebar:
   label: 'Spiral Matrix'
   badge: 'Medium'

apps/docs/content/(02-nodal-grid)/matrix-index-math/73-set-matrix-zeroes.mdx

@@ -1,7 +1,7 @@
 ---
 title: '73. Set Matrix Zeroes'
 description: Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0's
-icon: line-dot-left-horizontal
+icon: dot
 sidebar:
   label: 'Set Matrix Zeroes'
   badge: 'Medium'