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

instructions/dev/version-parts.md

@@ -66,7 +66,12 @@ a new one, and only `version release` turns it into something the release workfl
 
   1. **Heading, author, breaking/migration lines** - written by `version bump`, anchored right
      above the bump list so the line an operator most needs to act on never sits beneath a list
-     that can run long.
+     that can run long. The breaking line **accumulates** across a candidate's crossings - one
+     reason on the marker line, bullets under a bare marker from the second onward - because a
+     long-running candidate can break compatibility more than once and each break is its own
+     thing to act on. The migration line does not: it answers one yes/no about the candidate as
+     a whole, and `--migration-required` is its retraction path. Nothing retracts a breaking
+     reason; a wrong one is rare enough, and the candidate is dev-local until release.
   2. **The bump list**, grouped `**High/Medium/Low impact**` (empty groups omitted) - rendered by
      `version bump`'s `--impact` (default `medium`), corrected after the fact by `version regrade`.
      Flat and ungrouped, exactly as before this layering existed, when every bump is `medium` - the