Add events and relationships API (Phase 1: flesh out the graph)

Events (create/list-per-person/soft-delete) and relationships (create/list-per-person/soft-delete) through the layered stack: editor-gated writes, privacy-engine reads, audit on every change. Events carry exactly one subject (person XOR partnership); relationships are typed qualified edges (parent_child gets a biological/adoptive/step/foster/donor/guardian qualifier). Adds a single-person GET. 18 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/api/v1/persons.py

@@ -41,3 +41,14 @@ async def list_persons(
     tree = await tree_service.get_tree(session, viewer_id=current.id, tree_id=tree_id)
     persons = await person_service.list_persons(session, viewer_id=current.id, tree=tree)
     return [PersonRead.model_validate(p) for p in persons]
+
+
+@router.get("/{tree_id}/persons/{person_id}", response_model=PersonRead)
+async def get_person(
+    tree_id: uuid.UUID, person_id: uuid.UUID, session: SessionDep, current: CurrentUser
+) -> PersonRead:
+    tree = await tree_service.get_tree(session, viewer_id=current.id, tree_id=tree_id)
+    person = await person_service.get_person(
+        session, viewer_id=current.id, tree=tree, person_id=person_id
+    )
+    return PersonRead.model_validate(person)