Relationships: add field/fieldOn support for parent-side wikilink arrays

[mindsocket]

Problem

$metadata.relationships hardcodes 'parent' as the child-side field in both validation (validate-hierarchy.ts) and embedded parsing (parse-embedded.ts). This conflates relationship edges with hierarchy edges — parentNodeProps in _ost_tools_base.json defines parent as the hierarchy wikilink field, and it should remain reserved for that purpose.

Many schemas express relationships via parent-side wikilink arrays (e.g., Activity.tasks, Activity.outcomes). Previously these were silently skipped during relationship validation, and embedded nodes got a spurious parent field instead of populating the correct parent-side array.

The hierarchy edge system already supports field/fieldOn — relationships now have the same.

Solution

Added field (default: "parent") and fieldOn (default: "child") to RELATIONSHIP_SCHEMA.

fieldOn: "parent" (new)

• parse-embedded: child node gets no parent field; [[Child Title]] is appended to the semantic parent node's rel.field array
• validateRelationships: filters parent-type nodes; validates each rel.field array entry resolves to a node of rel.type

fieldOn: "child" (default, existing behaviour)

• parse-embedded: sets schemaData[rel.field ?? 'parent'] on child instead of hardcoded schemaData.parent
• validateRelationships: same logic, but uses rel.field ?? 'parent' instead of hardcoded 'parent'

Changes

• src/metadata-contract.ts — Added field and fieldOn to RELATIONSHIP_SCHEMA
• src/parse-embedded.ts — fieldOn: "parent" support for list and table embedded nodes
• src/validate-hierarchy.ts — validateRelationships() branches on fieldOn
• schemas/generated/_ost_tools_schema_meta.json — Regenerated
• tests/validate-relationships.test.ts — Tests for fieldOn: "parent", custom field name, and missing-field skip behaviour

Example schema usage

{
  "parent": "Activities",
  "type": "Tasks",
  "field": "tasks",
  "fieldOn": "parent",
  "format": "list",
  "matchers": ["Tasks", "Roles"],
  "multi": true
}

With this configuration:

• Embedded task items under an Activity's "Tasks" heading populate activity.tasks with [[Task Title]] wikilinks
• Validation checks that each entry in activity.tasks resolves to a node of type Tasks
• No spurious parent field is set on the task nodes

[mindsocket]

Completed in #52