feat: Prosa ist kein Identifier - Link-Taxonomie als Enum, generierte Regionen mit Markern (4.0.0)

Files changed:
- .gitea/workflows/ci.yml
- AGENTS.md
- CHANGES.md
- VERSION
- instructions/CONTRACT.md
- instructions/link-taxonomy.md
- instructions/migrations/4.0.0-link-taxonomy.md
- instructions/setup-instance.md
- kb/CONTRACT.md
- kb/CONVENTIONS.md
- kb/CONVENTIONS.md.template
- kb/comparisons/COLLECTION.md
- kb/concepts/COLLECTION.md
- kb/entities/COLLECTION.md
- kb/sources/COLLECTION.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/blocks.py
- tools/chemenu/cli.py
- tools/chemenu/commands/cite_cmd.py
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/links_cmd.py
- tools/chemenu/commands/migrate_cmd.py
- tools/chemenu/commands/new_page.py
- tools/chemenu/commands/page_ops.py
- tools/chemenu/commands/run_budget.py
- tools/chemenu/commands/xref.py
- tools/chemenu/conventions.py
- tools/chemenu/corpus_diff.py
- tools/chemenu/frontmatter_io.py
- tools/chemenu/kb_collections.py
- tools/chemenu/kb_state.py
- tools/chemenu/links.py
- tools/chemenu/lint_core.py
- tools/chemenu/provenance.py
- tools/chemenu/sections.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_blocks.py
- tools/chemenu/tests/test_cite_cmd.py
- tools/chemenu/tests/test_conventions.py
- tools/chemenu/tests/test_dist_cmd.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_migrate_cmd.py
- tools/chemenu/tests/test_new_page.py
- tools/chemenu/tests/test_pipeline_l0.py
- tools/chemenu/tests/test_types_cmd.py
- tools/chemenu/tests/test_xref.py
- types/concept.schema.yaml
- types/entity.md
- types/entity.schema.yaml
- types/instruction.schema.yaml
- types/type-spec.md
- work/link-taxonomy-migration/README.md
- work/link-taxonomy-migration/plan.md

kb/sources/COLLECTION.md

@@ -1,5 +1,7 @@
 ---
 profile: sources
+outbound:
+  any: [is-evidence-for, defined-in, see-also]
 required_by_stack: true
 ---
 
@@ -38,6 +40,17 @@ The `raw_files:`/`source_url:`/citation rules are shared and live in
 - `tools/wikitool sources trace --raw <path>` answers "what did we learn from this?";
   `tools/wikitool sources coverage` lists raw files no source page claims yet.
 
+## Authorised labels
+
+The `outbound:` block above is what `wikitool lint` and `xref add` check: which labels a page in
+this collection may use, per destination. The catalogue they are drawn from - and what each one
+asserts - is [instructions/link-taxonomy.md](../../instructions/link-taxonomy.md), which binds
+nothing on its own.
+
+Deliberately narrow. A source page is evidence *about* a source; almost everything it would want to say is already carried by `raw_files:`, `sources:` and `[^cite-id]`, which are the mechanical provenance path rather than authored edges.
+
+Adding a label here is a deliberate contract change, not a way around a refusal.
+
 ## Outbound linking
 
 A source page links to every entity and concept it produced or updated.