docs: add research domains and resource registry

- add local external resources registry
- add research domain contract and per-repository research domains
- add raw fact snapshot governance and validation scripts

Validation:
- make test
- git diff --check HEAD~1..HEAD

Note:
- welcome workflow failed because its action input names are stale; core content CI passed.

.gitignore

@@ -97,3 +97,6 @@ backups/gz/
 
 # Local-only enterprise architecture evidence kit
 assets/templates/modern-enterprise-architecture-private/
+
+# Local research repository clones
+docs/research/**/raw/repository/