Plain visual docs

If AGENTS.md sets a different convention for this topic, follow AGENTS.md.

A reader must understand the purpose in 30 seconds and the structure in 2 minutes. Text alone does not do that for most technical changes.

1. Plain-language opening

Start the document with a short section (## TL;DR in specs, ## In plain words in pull requests).

• Write for a reader who does not know the code, the jargon or this session.
• Describe the effect, not the mechanism. Write "too many wrong passwords and the sign-in waits a minute", not "rate limit of 5 requests per minute per IP".
• Cover: what changes, who uses it, what they can do, what stays the same, what is not included.
• One paragraph, or one sentence and up to eight bullets.
• Do not use: framework names, protocol names, acronyms, file names.

2. ASCII for structure

Use ASCII inside ```text fences for: