Update mutable template fields
1-100 chars after trimming). Must remain owner-unique.null to clear.private or workspace.visibility: "workspace" requires workspace scope.400 missing_template_id - path param missing400 invalid_json - body is not valid JSON422 invalid_payload - schema validation failed or body is empty404 not_found - template not found in readable scope403 forbidden_template - template exists but mutation is not allowed in current scope409 template_name_conflict - name already exists for owner422 invalid_template_config - provided config is invalid401 - authentication failed (missing/invalid/revoked token)402 subscription_required - active Creator/Professional/Business plan required403 tier_not_allowed - Scheduler tier cannot use Partner API500 template_update_failed - unexpected update failure