stack: Control-Plane-Sprache universell - Achse ist das Publikum, kein Instanz-Schalter (#103)

Files changed:
- AGENTS.md
- CHANGES.md
- VERSION
- docs/language-boundaries.md
- kb/CONVENTIONS.md
- kb/CONVENTIONS.md.template
- tools/chemenu/commands/dist_cmd.py

kb/CONVENTIONS.md

@@ -53,6 +53,12 @@ Two things follow from that value rather than being decided here, both stated on
 [AGENTS.md § File naming](../AGENTS.md#file-naming): the control plane stays English whatever an
 instance writes its pages in, and an agent *speaks* the language named above.
 
+The first of those is not a setting this file withholds - it is not a setting at all. `language:`
+above is the only language value in the tree, and what it binds is page text; a control-plane
+document is English even when this instance wrote it for itself and never ships it. Why that is
+an architecture decision rather than an unset parameter:
+[docs/language-boundaries.md](../docs/language-boundaries.md).
+
 Which line is prose and which is an identifier - and therefore what is translated at all - is
 the contract's rule, not this file's: see
 [kb/CONTRACT.md § Language and identifiers](CONTRACT.md#language-and-identifiers).