Phase 0 milestone 0.5: Registrant vertical slice

Registrant model + schemas + router + migration 0003, exercising the
vendored framework end-to-end (CRUDService, RBAC, audit, version history).

- SSN app-layer encrypted (AES-256-GCM, HKDF key, column-bound AAD,
  versioned format) in security/column_crypto.py; write-only on the model;
  serializer exposes only ssn_masked (XXX-XX-1234). C.5.7.50 / SC-28.
- pii_read audit on GET, list (one row per page with ids), and history.
  C.5.6.9 #5 / AU-14.
- Portal-only callers (YOUTH/PARENT/HOST) limited to own row via
  Registrant.user_id; out-of-scope is 404. PARENT_USER sees nothing until
  Guardian lands. History gated on VersionHistory, not View.
- minor_flag derived from dob at read time.

Framework changes (flag to OWC on re-vendor):
- crud._to_dict honors __audit_redact__, keeping ciphertext out of
  audit_log and version_history.
- crud._to_dict serializes date (not only datetime) for JSON columns.
- CRUDService.history annotation uses builtins.list (method shadowed it).

98 tests passing, 94.83% coverage; ruff + mypy clean.
Coverage trace at docs/coverage/registrant.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

migrations/versions/0003_registrants.py

@@ -0,0 +1,71 @@
+"""Registrants table — Phase 0 vertical slice.
+
+Revision ID: 0003_registrants
+Revises: 0002_framework_tables
+Create Date: 2026-09-30
+
+Milestone 0.5. ARCHITECTURE.md §6.1 / PHASE0_PLAN.md §4.
+
+- `ssn_encrypted` holds AES-256-GCM ciphertext from security/column_crypto.py
+  (NIST SC-28; source RFP `C.5.7.50`). Never plaintext.
+- `ssn_last4` is the only SSN-derived value stored in the clear — for search
+  and masked display (``XXX-XX-1234``).
+- No `minor_flag` column: derived from `dob` at read time.
+- `user_id` links the youth's own portal account (Phase 1 account-link flow).
+
+Per repo rule (CONTRIBUTING.md): this file is immutable once merged.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0003_registrants"
+down_revision: str | Sequence[str] | None = "0002_framework_tables"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "registrants",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("first_name", sa.String(length=100), nullable=False),
+        sa.Column("middle_name", sa.String(length=100), nullable=True),
+        sa.Column("last_name", sa.String(length=100), nullable=False),
+        sa.Column("dob", sa.Date(), nullable=False),
+        sa.Column("ssn_encrypted", sa.String(length=255), nullable=True),
+        sa.Column("ssn_last4", sa.String(length=4), nullable=True),
+        sa.Column("email", sa.String(length=255), nullable=True),
+        sa.Column("phone", sa.String(length=32), nullable=True),
+        sa.Column("address_line1", sa.String(length=255), nullable=True),
+        sa.Column("address_line2", sa.String(length=255), nullable=True),
+        sa.Column("city", sa.String(length=100), nullable=True),
+        sa.Column("state", sa.String(length=2), nullable=True),
+        sa.Column("zip", sa.String(length=10), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("version", sa.Integer(), nullable=False, server_default=sa.text("1")),
+    )
+    op.create_index("ix_registrants_user_id", "registrants", ["user_id"])
+    op.create_index("ix_registrants_last_name", "registrants", ["last_name"])
+    op.create_index("ix_registrants_dob", "registrants", ["dob"])
+    op.create_index("ix_registrants_ssn_last4", "registrants", ["ssn_last4"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_registrants_ssn_last4", table_name="registrants")
+    op.drop_index("ix_registrants_dob", table_name="registrants")
+    op.drop_index("ix_registrants_last_name", table_name="registrants")
+    op.drop_index("ix_registrants_user_id", table_name="registrants")
+    op.drop_table("registrants")