Alternate names (maiden/married), self-person link, deletion integrity

Names (the genealogy standard: maiden name primary, married/alias as typed
alternates):
- Name model already supported multiple typed names; expose full CRUD —
  NameCreate/Read/Update schemas, name_service (one-primary invariant,
  promote-on-delete), nested /persons/{id}/names routes.
- Person page gains a Names card: add/edit/delete + "make primary", with a
  curated name_type dropdown (birth/maiden, married, alias, nickname, …).

Self-person ("who am I"):
- users.self_person_id FK (use_alter for the users<->persons<->trees cycle)
  + migration; PATCH /users/me/self-person; "This is me" / "This is you"
  on the person page. Soft-deleting the linked person clears it.

Deletion integrity (fixes the broken tree view):
- delete_person now soft-deletes the relationships touching the person, so no
  dangling edges remain; family-chart also filters links to missing people.
- Optional cascade=true recursively deletes descendants (GEDCOM cleanup);
  the person page asks "only this person" vs "with all descendants".
- DELETE returns {deleted: n}.

Family view surfaces "Not connected to anyone" so dangling people aren't lost.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/v1/users.py

@@ -1,7 +1,8 @@
 from fastapi import APIRouter
 
-from app.api.deps import CurrentUser
-from app.schemas.user import UserRead
+from app.api.deps import CurrentUser, SessionDep
+from app.schemas.user import UserRead, UserSelfPersonUpdate
+from app.services import user_service
 
 router = APIRouter(prefix="/users", tags=["users"])
 
@@ -9,3 +10,14 @@ router = APIRouter(prefix="/users", tags=["users"])
 @router.get("/me", response_model=UserRead)
 async def read_me(current: CurrentUser) -> UserRead:
     return UserRead.model_validate(current)
+
+
+@router.patch("/me/self-person", response_model=UserRead)
+async def set_self_person(
+    data: UserSelfPersonUpdate, session: SessionDep, current: CurrentUser
+) -> UserRead:
+    """Link (or unlink) the Person record that represents this account."""
+    user = await user_service.set_self_person(
+        session, user=current, person_id=data.self_person_id
+    )
+    return UserRead.model_validate(user)