stack: TOC-Scope auf types/ und docs/, Sprachregeln nach AGENTS.md zentralisiert, alle Templates auf Control-Plane-Sprache, --breaking akkumuliert (schliesst #99)

Files changed:
- AGENTS.md
- CHANGES.md
- ENVIRONMENT.md.template
- SOUL.md
- SOUL.md.template
- USER.md.template
- VERSION
- docs/ownership-and-templates.md
- docs/version-model.md
- instructions/CONTRACT.md
- instructions/dev/doc-pull-through.md
- instructions/dev/stack-close/SKILL.md
- instructions/dev/stack-dev/SKILL.md
- instructions/dev/version-parts.md
- instructions/setup-instance.md
- kb/CONVENTIONS.md
- kb/CONVENTIONS.md.template
- kb/concepts/COLLECTION.md
- kb/sources/COLLECTION.md
- tools/CONTRACT.md
- tools/chemenu/commands/types_cmd.py
- tools/chemenu/commands/version_cmd.py
- tools/chemenu/tests/test_toc.py
- tools/chemenu/tests/test_version_cmd.py
- tools/chemenu/toc.py
- tools/chemenu/version.py
- types/comparison.md
- types/concept.md
- types/entity.md
- types/lint-report.md
- types/source.md

kb/CONVENTIONS.md

@@ -40,11 +40,18 @@ those regions and nothing else. Nothing matches on this text.
 
 ## Language
 
-Pages are written in **German**. This binds `kb/` and the authoring surface that shapes it -
-the page type-specs `types/entity.md`, `types/concept.md`, `types/source.md` and
-`types/comparison.md`. `raw/` is untouched ([raw/CONTRACT.md](../raw/CONTRACT.md)), and the
-control plane stays English: `AGENTS.md`, the stage contracts, this file, `instructions/`, and
-the type-specs for non-page artifacts.
+Pages are written in **German** - the `language:` in this file's own frontmatter, and the one
+place that value is written down. This binds `kb/`, and inside the page type-specs
+(`types/entity.md`, `types/concept.md`, `types/source.md`, `types/comparison.md`) exactly the
+parts that become page text: each one's `## Template` block, and the `layout:` titles that head a
+catalog section. Their authoring guidance around those is instruction to an agent, so it follows
+the control plane and stays English - the same prose/identifier cut
+[kb/CONTRACT.md](CONTRACT.md#language-and-identifiers) makes inside a page, applied one level up.
+`raw/` is untouched ([raw/CONTRACT.md](../raw/CONTRACT.md)).
+
+Two things follow from that value rather than being decided here, both stated once in
+[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.
 
 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