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

backend/app/schemas/organizations.py

@@ -0,0 +1,29 @@
+from pydantic import BaseModel
+
+
+class OrganizationCreateRequest(BaseModel):
+    org_code: str
+    name: str
+    tax_id: str | None = None
+    status: str = "active"
+
+
+class OrganizationUpdateRequest(BaseModel):
+    name: str | None = None
+    tax_id: str | None = None
+    status: str | None = None
+
+
+class OrganizationSummary(BaseModel):
+    id: str
+    org_code: str
+    name: str
+    tax_id: str | None = None
+    status: str
+
+
+class OrganizationListResponse(BaseModel):
+    items: list[OrganizationSummary]
+    total: int
+    limit: int
+    offset: int