feat(psa): add PsaMemberMapping model and migration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic/versions/061_add_psa_member_mappings.py

@@ -0,0 +1,60 @@
+"""Add psa_member_mappings table for user-to-CW-member mapping.
+
+Revision ID: 061
+Revises: 060
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = "061"
+down_revision = "060"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "psa_member_mappings",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column(
+            "psa_connection_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("psa_connections.id", ondelete="CASCADE"),
+            nullable=False,
+            index=True,
+        ),
+        sa.Column(
+            "user_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("external_member_id", sa.String(100), nullable=False),
+        sa.Column("external_member_name", sa.String(200), nullable=False),
+        sa.Column("matched_by", sa.String(50), nullable=False),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+        sa.UniqueConstraint(
+            "psa_connection_id", "user_id",
+            name="uq_psa_member_mapping_connection_user",
+        ),
+        sa.UniqueConstraint(
+            "psa_connection_id", "external_member_id",
+            name="uq_psa_member_mapping_connection_member",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("psa_member_mappings")