Accept the reality nobody looks at the C4 model diagrams: remove them

Overview

~1.5 year ago, in 📌 [PP-1] Diagram tying the product requirements + decisions together Postponed , after DrupalCon Pittsburgh, I introduced C4 model diagrams (see https://c4model.com). Thanks to strong encouragement by Kyle aka @ctrlADel

I still agree with Kyle that this is a valuable way to explain Canvas, what purpose does it serve, how does it work, who is it intended to serve, etc. It's superb that it's versioned, text-based, and can generate visual diagrams 🤩

I also think it is a great communication tool between:

1. Product (Owner/Manager — to keep a high-level technical overview, and understand what a certain new feature would require)
2. Engineering (all of us writing the code, to stay aligned on how it works)
3. the community at large (those who consider adopting Canvas, and want to understand how it works)

I had hoped that this would be the way that Product would be conveying expectations for upcoming features.

Unfortunately:

• to my knowledge, not a single person has looked at these or used them as a reference
• to my knowledge, not a single has updated them besides me
• the CI job has been broken since October 10, 2025
• (the fact that nobody has bothered to even fix CI is further indication that nobody cares)
• the last significant update was 7 months ago: [#34452581]

Proposed resolution

There seems no practical value in maintaining these. So remove them.

We can restore them if we change our mind.

User interface changes

None.