Process Session Campaign

Read the optimisation-campaign ledger for a cloud-process session.

core exposes it at GET /api/campaign/{session_id} (the ledger the organism workbench renders). The SPA's sessionFetch('/api/campaign/<sid>') becomes /api/processes/<pid>/campaign/<sid> for a process-bound conversation, and this relays it down the process's WS socket via the same _process_rpc bridge as plan/memory/goal. session_id is re-encoded rather than forwarded raw so an id needing escaping can't reshape the core path. A session with no campaign is {"campaign": null} with 200 from core — not an error.