The fleet graph redraws when the event stream says spend or runs moved, never on a 30 s timer #3161

Part of #2676 (stream, never poll). src/web/fleet-graph.ts redraws with setInterval(…, FLEET_GRAPH_REFRESH_MS) (30 s).

Done:

• [ ] The interval and FLEET_GRAPH_REFRESH_MS are gone; the graph redraws on the page's existing live stream when an event that moves spend or runs arrives, coalesced to at most one redraw a second, and on visibilitychange to visible as today.
• [ ] A test greps the client script and finds no setInterval; another asserts the events that trigger a redraw are named in one list.

Files: src/web/fleet-graph.ts, its test. Risk: a quiet forge never redraws; that is correct, say it in a comment.