CAT-K5: a section is a part with a plain title, never a file; a reference has one form

A new rule, section-form (31 now), refuses from the day the records move a section whose title is a file name, a number
prefix, a slash or over 200 bytes, a title twice in a record, and a text that holds a local path, a file and line, or a
link to a file. Only a section that is new or changed is judged, so a record imported with file-named sections keeps
them until its form-only version; write refuses at once.

Issue 1966.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/mesh-knowledge/README.md

@@ -77,7 +77,7 @@ as text. `get` serves each, and any other field a record of hq wrote under `fiel
 ## Writing a record
 
 1. `reserve` a number for its kind.
-2. `propose` the record whole. It is refused, naming every reason at once, when it breaks one of the **30 rules
+2. `propose` the record whole. It is refused, naming every reason at once, when it breaks one of the **31 rules
    that judge one record or its prose**. They are hq's checks moved to the write; `PerRecordRules` in `rules.go`
    lists each one with the check it comes from:
    - 25 on the structure: kind, reserved number, title, topic, date, deciders, research status, at least one