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/models/user.py

@@ -3,9 +3,10 @@ multiple auth providers later (the provider-link table arrives with the auth
 slice). ``hashed_password`` is nullable: external/OIDC users have none.
 """
 
+import uuid
 from datetime import datetime
 
-from sqlalchemy import DateTime, String
+from sqlalchemy import DateTime, ForeignKey, String
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.models.base import Base
@@ -19,3 +20,15 @@ class User(Base, UUIDPrimaryKey, Timestamps, SoftDelete):
     email_verified_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     display_name: Mapped[str | None] = mapped_column(String(255))
     hashed_password: Mapped[str | None] = mapped_column(String(255))
+    # The Person record that *is* this user ("home person"). Cleared if that
+    # person is deleted, so the link can never dangle.
+    self_person_id: Mapped[uuid.UUID | None] = mapped_column(
+        # use_alter + explicit name: users<->persons<->trees form an FK cycle,
+        # so this constraint must be created/dropped via ALTER, not inline.
+        ForeignKey(
+            "persons.id",
+            ondelete="SET NULL",
+            name="fk_users_self_person_id",
+            use_alter=True,
+        )
+    )