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/RouteErrorBoundary.tsx

@@ -0,0 +1,76 @@
+/**
+ * @file RouteErrorBoundary.tsx
+ * @description Route-level error boundary around the lazily loaded pages. After
+ * a self-update an open tab still asks for the OLD `/assets/<Page>-<hash>.js`,
+ * which the SPA fallback answers with index.html, so the dynamic import
+ * rejects: that case reloads the page once (a sessionStorage guard stops a
+ * reload loop). Any other render error — or a second chunk failure — shows a
+ * themed "Something went wrong — Reload" panel instead of a blank app.
+ * `reloadOnce` is also used by App's `vite:preloadError` listener.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { Component, type ReactNode } from "react";
+import i18n from "../i18n";
+
+const RELOAD_KEY = "agenthub.chunkReloadAt";
+/** A second chunk failure within this window means the reload did not help. */
+const RELOAD_WINDOW_MS = 30_000;
+
+/** A failed dynamic `import()` (Chrome, Firefox, Safari wordings) or a ChunkLoadError. */
+export function isChunkLoadError(err: unknown): boolean {
+  if (!(err instanceof Error)) return false;
+  return (
+    err.name === "ChunkLoadError" ||
+    /dynamically imported module|Importing a module script failed|error loading dynamically imported module|Unable to preload CSS/i.test(
+      err.message
+    )
+  );
+}
+
+/** Reload the page unless this tab already did so in the last 30 s. */
+export function reloadOnce(reload: () => void = () => window.location.reload()): boolean {
+  try {
+    const last = Number(sessionStorage.getItem(RELOAD_KEY) || 0);
+    if (Date.now() - last < RELOAD_WINDOW_MS) return false;
+    sessionStorage.setItem(RELOAD_KEY, String(Date.now()));
+  } catch {
+    return false; // no sessionStorage: no loop guard, so never auto-reload
+  }
+  reload();
+  return true;
+}
+
+interface Props {
+  children: ReactNode;
+  /** Injected in tests; defaults to `window.location.reload`. */
+  reload?: () => void;
+}
+
+export class RouteErrorBoundary extends Component<Props, { error: Error | null }> {
+  state = { error: null as Error | null };
+
+  static getDerivedStateFromError(error: Error) {
+    return { error };
+  }
+
+  componentDidCatch(error: Error) {
+    if (isChunkLoadError(error)) reloadOnce(this.props.reload);
+  }
+
+  render() {
+    if (!this.state.error) return this.props.children;
+    const reload = this.props.reload ?? (() => window.location.reload());
+    return (
+      <div role="alert" className="card flex flex-col items-center gap-3 py-16 text-center">
+        <p className="text-sm font-medium text-fg-primary">
+          {i18n.t("dashboard:errorBoundary.title")}
+        </p>
+        <p className="text-xs text-fg-muted max-w-md">{i18n.t("dashboard:errorBoundary.body")}</p>
+        <button type="button" className="btn-primary text-sm" onClick={reload}>
+          {i18n.t("dashboard:errorBoundary.reload")}
+        </button>
+      </div>
+    );
+  }
+}