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/tree.py

@@ -0,0 +1,43 @@
+"""Tree — the top-level tenant boundary for genealogical data — and
+TreeMembership, the basis for authorization (ARCHITECTURE §5).
+"""
+
+import uuid
+
+from sqlalchemy import Enum as SAEnum
+from sqlalchemy import ForeignKey, String, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.models.base import Base
+from app.models.enums import MembershipRole, TreeVisibility
+from app.models.mixins import SoftDelete, Timestamps, UUIDPrimaryKey
+
+
+class Tree(Base, UUIDPrimaryKey, Timestamps, SoftDelete):
+    __tablename__ = "trees"
+
+    owner_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("users.id", ondelete="RESTRICT"), index=True
+    )
+    name: Mapped[str] = mapped_column(String(255))
+    description: Mapped[str | None] = mapped_column(Text)
+    visibility: Mapped[TreeVisibility] = mapped_column(
+        SAEnum(TreeVisibility, name="tree_visibility"),
+        default=TreeVisibility.private,
+        server_default=TreeVisibility.private.value,
+    )
+
+
+class TreeMembership(Base, UUIDPrimaryKey, Timestamps):
+    __tablename__ = "tree_memberships"
+    __table_args__ = (
+        UniqueConstraint("tree_id", "user_id", name="uq_tree_memberships_tree_user"),
+    )
+
+    tree_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("trees.id", ondelete="CASCADE"), index=True
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), index=True
+    )
+    role: Mapped[MembershipRole] = mapped_column(SAEnum(MembershipRole, name="membership_role"))