feat: add organization and member management APIs for admin and internal use

app/repositories/member_organizations_repo.py

@@ -0,0 +1,43 @@
+from sqlalchemy import delete, select
+from sqlalchemy.orm import Session
+
+from app.models.member_organization import MemberOrganization
+from app.models.organization import Organization
+
+
+class MemberOrganizationsRepository:
+    def __init__(self, db: Session) -> None:
+        self.db = db
+
+    def list_organizations_by_member_id(self, member_id: str) -> list[Organization]:
+        stmt = (
+            select(Organization)
+            .join(MemberOrganization, MemberOrganization.organization_id == Organization.id)
+            .where(MemberOrganization.member_id == member_id)
+            .order_by(Organization.name.asc())
+        )
+        return list(self.db.scalars(stmt).all())
+
+    def add_if_not_exists(self, member_id: str, organization_id: str) -> MemberOrganization:
+        stmt = select(MemberOrganization).where(
+            MemberOrganization.member_id == member_id,
+            MemberOrganization.organization_id == organization_id,
+        )
+        existing = self.db.scalar(stmt)
+        if existing:
+            return existing
+
+        relation = MemberOrganization(member_id=member_id, organization_id=organization_id)
+        self.db.add(relation)
+        self.db.commit()
+        self.db.refresh(relation)
+        return relation
+
+    def remove(self, member_id: str, organization_id: str) -> int:
+        stmt = delete(MemberOrganization).where(
+            MemberOrganization.member_id == member_id,
+            MemberOrganization.organization_id == organization_id,
+        )
+        result = self.db.execute(stmt)
+        self.db.commit()
+        return int(result.rowcount or 0)