Request background analytics refresh

Queue a workspace analytics refresh and return immediately. Requests are deduplicated while a job is active, with a five-minute start cooldown. Optional ifStale=true reuses a collection updated within fifteen minutes; the dashboard uses it once on entry without restarting collection on filter changes. Recent eligible content is checked first through bounded continuations on a separate queue. During reliability incidents, collection can be paused: new requests return 503, analytics_refresh_unavailable and Retry-After: 60. Stored reports remain available. The same explicit refresh operation is available through get_analytics with refresh=true in MCP.