feat(dashboard): lazy routes, Needs-you strip, URL state, exact numbers

- Workspace, SettingsHub, SessionDetail and the Workflow sub-tab are lazy
  (main bundle 2,166 kB -> ~920 kB), wrapped in RouteErrorBoundary: a stale
  chunk after a self-update reloads once (vite:preloadError too), any other
  error shows a Reload panel instead of a blank page.
- Live refresh: lib/throttle.ts + hooks/useLiveRefresh.ts replace trailing
  debounces that froze under a steady event stream; refresh skips hidden
  tabs and refetches after a WebSocket reconnect. Monitor loads only while
  shown, with one batched GET /api/agents?session_ids= instead of N+1; a
  failing endpoint is an inline error, not a blank Dashboard.
- NeedsYouStrip on Monitor and above Analytics. Tabs, filters, page, sort
  and search live in the URL (Dashboard, Sessions, Activity, SessionDetail).
- Sessions: tool / workspace / date-range filters, CSV/JSON export
  (formula-neutralised), focusable row links, Open in workspace (the dead
  /run links are gone), stale responses dropped, error + Retry.
- Fixes: "NaNs" durations, 30/7-day charts skipping idle days, weekday
  labels west of UTC (now averages), cache hit rate denominator, billable
  tokens vs cache reads, exact tool-call counts, "To" date = end of day,
  invalid ?from= no longer throws, recent list no longer shrinks to 15,
  stable message keys, transcript switch races.
- Light-theme-unreadable bg-black code panels and dark-only DAG fills use
  tokens; status configs and chart colours use theme tokens; Health tab
  and other literals translated.
- Server (additive): GET /api/agents?session_ids=, GET /api/sessions
  awaiting=1&from=&to=, stats tool_call_count/distinct_tool_count, event
  rows carry session/agent labels.

client/src/components/workflows/SkillUsagePanel.tsx

@@ -12,7 +12,7 @@
 import { useCallback, useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { api } from "../../lib/api";
-import { eventBus } from "../../lib/eventBus";
+import { useLiveRefresh } from "../../hooks/useLiveRefresh";
 import type { SkillUsage } from "../../lib/types";
 
 export function SkillUsagePanel({ statusFilter }: { statusFilter: string }) {
@@ -33,17 +33,10 @@ export function SkillUsagePanel({ statusFilter }: { statusFilter: string }) {
     void refresh();
   }, [refresh]);
 
-  useEffect(() => {
-    let timer: ReturnType<typeof setTimeout>;
-    const unsub = eventBus.subscribe(() => {
-      clearTimeout(timer);
-      timer = setTimeout(() => void refresh(), 3000);
-    });
-    return () => {
-      unsub();
-      clearTimeout(timer);
-    };
-  }, [refresh]);
+  // Throttled (not debounced): a steady event stream still refreshes every 3 s.
+  useLiveRefresh(() => void refresh(), {
+    match: (msg) => msg.type === "new_event" || msg.type === "session_updated",
+  });
 
   if (error) return <p className="text-xs text-status-danger">{error}</p>;
   if (!data) return null;