Add "about" modal

[falgon]

• Add a modal on top page in the left sidebar that displays a diagram showing the general structure (site map) of the entire roki.dev and a table showing system update records:

  graph TD;
  s[roki.dev]
  s[roki.dev]---b1[roki.log]
  s---b2[roki.diary]
  s---r[resume]
  subgraph "Blogs"
  b1
  b2
  end
  click s "https://roki.dev"
  click b1 "https://roki.dev/roki.log"
  click b2 "https://roki.dev/roki.diary"
  click r "https://roki.dev/resume"

• be able to render mermaid figures #567
• The system update table is written in markdown format:
  • summary
  • PR
  • date
  • ...