Add core data model (12 tables) and initial Alembic migration

All core entities from ARCHITECTURE §5: tenancy (User, Tree, TreeMembership), people (Person, Name, Relationship), facts (Event, Place, PlaceName), provenance (Source, Citation), and the append-only AuditEntry. Cross-cutting mixins give every row a UUID key, timestamps, soft delete, and (where tree-owned) a tree_id for uniform tenant isolation.

Modeling choices: parentage as qualified edges (biological/adoptive/step/foster/donor/guardian) so non-traditional families are first-class; events keep both a verbatim date string and a normalized start/end range; closed sets are PG enums while GEDCOM-extensible vocabularies (event/name/source type) stay strings; CHECK constraints enforce single-subject events and single-target citations. Place is tree-scoped in Phase 0 (see ARCHITECTURE note). The migration is verified reversible (upgrade/downgrade drops tables and enum types) and matches the models (alembic check clean); applied on the deploy target. Dockerfile now ships migrations.

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

backend/app/models/relationship.py

@@ -0,0 +1,40 @@
+"""Relationship — a typed, qualified edge between two Persons.
+
+Modeling parentage as qualified edges (rather than assuming two biological
+parents) is what makes adoption, donor conception, and blended families
+first-class. ``qualifier`` applies to parent_child edges; partnership events
+(marriage, divorce) attach to the Relationship via Event.relationship_id.
+"""
+
+import uuid
+
+from sqlalchemy import CheckConstraint, ForeignKey, Text
+from sqlalchemy import Enum as SAEnum
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.models.base import Base
+from app.models.enums import ParentChildQualifier, RelationshipType
+from app.models.mixins import SoftDelete, TenantScoped, Timestamps, UUIDPrimaryKey
+
+
+class Relationship(Base, UUIDPrimaryKey, TenantScoped, Timestamps, SoftDelete):
+    __tablename__ = "relationships"
+    __table_args__ = (
+        CheckConstraint("person_from_id <> person_to_id", name="different_persons"),
+    )
+
+    type: Mapped[RelationshipType] = mapped_column(
+        SAEnum(RelationshipType, name="relationship_type")
+    )
+    # For parent_child: from = parent, to = child. For partnership/sibling: symmetric.
+    person_from_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("persons.id", ondelete="CASCADE"), index=True
+    )
+    person_to_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("persons.id", ondelete="CASCADE"), index=True
+    )
+    # Only meaningful for parent_child edges.
+    qualifier: Mapped[ParentChildQualifier | None] = mapped_column(
+        SAEnum(ParentChildQualifier, name="parent_child_qualifier")
+    )
+    notes: Mapped[str | None] = mapped_column(Text)