Use final AsDecided repository paths

[tcballard]

Summary

• point the specification at asdecided/spec and reference implementation at asdecided/core
• update raw schema IDs to the final organization and repository paths
• identify the maintainer by the personal @tcballard account rather than the retired organization login

Compatibility boundary

The stable RAC vocabulary, artifact IDs, schema keys, and normative conformance behavior are unchanged. The authoritative artifact_specs and relationship_descriptions JSON values match main exactly.

Verification

• all JSON documents parse
• authoritative contract payload matches main
• no stale itsthelore/asdecided-* or doubled asdecided/asdecided-* paths remain
• git diff --check passes