Add triage muse agent and synchronous triage API endpoint
New `muse/triage.md` cogitate agent for quick-action chat bar requests
(navigate, todos, calendar, entities). Uses `instructions: {"now": true}`
only — no journal context, no facet injection from compose_instructions.
New `POST /app/chat/api/triage` endpoint spawns the triage agent, waits
for completion (60s timeout), and returns the response synchronously.
Triage responses are ephemeral — no chat records created.