Add 'tooling' category to Repo Classification Standard

Insert a 'tooling' category between project and product (reusable internal
tooling/infrastructure: libraries, CLIs, services, ops components used across
the ecosystem rather than offered to external customers). Update §5 definition,
§11 decision procedure, §16 agent prompt, the machine-readable allowed-values,
and the CUST-WP-0050 T02 progress note. Nine custodian tooling repos
reclassified to it; the-custodian and inter-hub remain research.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

canon/standards/repo-classification.allowed.yaml

@@ -17,6 +17,7 @@ categories:
   - experimental
   - research
   - project
+  - tooling
   - product
   - business