Return clear error on user delete FK violation

Deleting a membership profile referenced by other tables (owner,
approver, assignee, etc.) surfaced as a generic Internal error.
Detect the Postgres FK violation (23503) in the coredata Delete,
return ErrResourceInUse, and map it to CONFLICT in the GraphQL
and MCP resolvers so the client sees an actionable error.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/server/api/mcp/v1/schema.resolvers.go

@@ -2574,6 +2574,9 @@ func (r *Resolver) RemoveUserTool(ctx context.Context, req *mcp.CallToolRequest,
 		if _, ok := errors.AsType[*iam.ErrLastActiveOwner](err); ok {
 			return nil, types.RemoveUserOutput{}, fmt.Errorf("cannot remove last active owner: %w", err)
 		}
+		if errors.Is(err, coredata.ErrResourceInUse) {
+			return nil, types.RemoveUserOutput{}, fmt.Errorf("cannot remove user: %w", err)
+		}
 
 		return nil, types.RemoveUserOutput{}, fmt.Errorf("remove user: %w", err)
 	}