feat(webui): live-update topology fan tiles without a page reload

Each fan tile carries data-fan / data-ceil / data-measured and a small
script polls /api/metrics/latest every 5s — the metrics collector's own
sampling period, served from memory with no extra BMC call — updating
each tile's spin rate, duty fill and tooltip in place. Polling faster
would only re-read identical numbers; sampling the BMC faster would
choke it under load. FanReading gains json tags for the endpoint.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VHG21rgTUiR1G3qFHTVmN

audit/internal/webui/page_topo_test.go

@@ -206,6 +206,13 @@ func TestTopoPageRendersCoolingFansAsFlexRow(t *testing.T) {
 	if !strings.Contains(body, "ceiling not measured") {
 		t.Fatalf("topo fan tooltip should note the ceiling is unmeasured: %s", body)
 	}
+	// Live-update: each tile is addressable and the poll script is present.
+	if n := strings.Count(body, `class="topo-fan-tile"`); n != 2 {
+		t.Fatalf("expected 2 addressable fan tiles, got %d", n)
+	}
+	if !strings.Contains(body, `data-fan="FAN1"`) || !strings.Contains(body, "/api/metrics/latest") {
+		t.Fatalf("topo fan row missing live-update wiring: %s", body)
+	}
 
 	// Component-detail fallback endpoint must resolve the "fan" type.
 	rec2 := httptest.NewRecorder()