FEAT-011: app.route.add passes created_by_agent_id=None instead of host-operator (SC-010 parity)

[brettheap]

Source: FEAT-011 Polish checkpoint (tasks.md §250) — SC-010 parity gap.

app.route.add passes created_by_agent_id=None to the FEAT-010 routes service, whereas the legacy CLI attributes route creation to "host-operator". This is a byte-level parity gap vs SC-010.

This is now a sharper inconsistency: app.send_input already attributes the host operator correctly via HOST_OPERATOR_SENTINEL (_host_operator_sender()), but route.add still hardcodes None.

Location: src/agenttower/app_contract/mutations.py:1536.

Fix: pass HOST_OPERATOR_SENTINEL (or the CLI's "host-operator" literal) as created_by_agent_id.