Switch all cross-service relation calls to the new registry-aware
relate/unrelate/can-relate actions, and consolidate per-service
container-nav fragment fetches into the generic relations handler.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Declarative relation registry via defrelation s-expressions with
cardinality enforcement (one-to-one, one-to-many, many-to-many),
registry-aware relate/unrelate/can-relate API endpoints, generic
container-nav fragment, and relation-driven UI components.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
