docs(content): add issue URLs to problem pages and restructure guides into appendix

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

@@ -7,6 +7,7 @@ topics:
   - { name: "Math", slug: "math" }
   - { name: "Matrix", slug: "matrix" }
 video: "fMSJSS7eO1w"
+issue: "https://github.com/prdlk/leetcode/issues/91"
 sidebar:
   label: 'Rotate Image'
   badge: 'Medium'

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

@@ -7,6 +7,7 @@ topics:
   - { name: "Matrix", slug: "matrix" }
   - { name: "Simulation", slug: "simulation" }
 video: "BJnMZNwUk1M"
+issue: "https://github.com/prdlk/leetcode/issues/92"
 sidebar:
   label: 'Spiral Matrix'
   badge: 'Medium'

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

@@ -7,6 +7,7 @@ topics:
   - { name: "Hash Table", slug: "hash-table" }
   - { name: "Matrix", slug: "matrix" }
 video: "T41rL0L3Pnw"
+issue: "https://github.com/prdlk/leetcode/issues/93"
 sidebar:
   label: 'Set Matrix Zeroes'
   badge: 'Medium'