Draft: Add architecture diagrams PNG files

What does this MR do and why?

There's been numerous reports over the years about the architecture diagram and how it's difficult to visualize it in the small real estate of the page.

This MR adds architecture diagrams PNG files that users can click and view/download, and a script to update those automatically. Also a test to check if any mermaid diagram is added or deleted.

PS. Claude helped me craft this script.

Related issues

• Docs feedback: Unable to read or open Gitlab Ar... (#523890)
• Rework GitLab architecture diagrams (#462508)

How to set up and validate locally

1. Check out this branch.
2. Run the script to create and compress the images:

   ./scripts/create-architecture-diagrams-png.rb
   
   
   INFO: Creating PNGs from the mermaid diagrams in 'doc/development/architecture.md'...
   Found 4 mermaid charts in Markdown input
   ✅ ./architecture_diagram-3.png
   ✅ ./architecture_diagram-4.png
   ✅ ./architecture_diagram-1.png
   [vue-sequence] Store is a function and is not initiated in 1 second.
   ✅ ./architecture_diagram-2.png
   Skipping already versioned file: architecture_diagram-1_v18_2.png
   Renamed: architecture_diagram-1.png → architecture_diagram-1_v18_2.png
   Skipping already versioned file: architecture_diagram-2_v18_2.png
   Renamed: architecture_diagram-2.png → architecture_diagram-2_v18_2.png
   Skipping already versioned file: architecture_diagram-3_v18_2.png
   Renamed: architecture_diagram-3.png → architecture_diagram-3_v18_2.png
   Skipping already versioned file: architecture_diagram-4_v18_2.png
   Renamed: architecture_diagram-4.png → architecture_diagram-4_v18_2.png
   INFO: Updating image references in architecture.md...
   Reference already up to date: architecture_diagram-1_v18_2.png
   Reference already up to date: architecture_diagram-2_v18_2.png
   Reference already up to date: architecture_diagram-3_v18_2.png
   Reference already up to date: architecture_diagram-4_v18_2.png
   INFO: Compressing the created images...
   Compressing 4 PNG files
   /Users/axil/devel/gitlab/gdk/gitlab/doc/development/img/architecture_diagram-4_v18_2.png was reduced by 28630 bytes
   /Users/axil/devel/gitlab/gdk/gitlab/doc/development/img/architecture_diagram-3_v18_2.png was reduced by 34638 bytes
   /Users/axil/devel/gitlab/gdk/gitlab/doc/development/img/architecture_diagram-1_v18_2.png was reduced by 34661 bytes
   /Users/axil/devel/gitlab/gdk/gitlab/doc/development/img/architecture_diagram-2_v18_2.png was reduced by 557416 bytes
   INFO: Cleaning up old image files...
   No old image files to remove.

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